Existentialism is a theory that makes life possible. The "possibility" here can be understood as a term "transcendence" by Sartre. Human action is transcendental, that is, it is always conceived in the present, and we try to realize it in the present. In other words, we have hope. It opens up the possibility of choice for mankind. Sartre said that existence precedes essence, and there are two kinds of existentialism, one is the existence of Christianity. The other is the atheistic existentialism of him and Heidegger. After denying the existence of God or suspending God, atheists put forward a proposition about human beings, that is, existence precedes essence. Essence precedes existence, which can be understood as purpose precedes existence. Sartre explained this proposition with "God is a craftsman who made man". Before the craftsman made tools, people had made clear his purpose. For what purpose, what tools were produced. Similarly, God created man. Human nature precedes human existence. Sartre denied the substitutes after God was destroyed, such as practical reason and absolute spirit. The death of God originated from Nietzsche. However, although Nietzsche denied God's stipulation on man, he still proposed a world schema (metaphysical remnants) to stipulate man. This model is eternal reincarnation. The first principle of existentialism is that human beings are just what they think. People come first. Then choose the purpose. Man is absolutely free. Arbitrary and arbitrary fetters gain arbitrary freedom from existence. Existence itself is freedom. If all God's rules on people are removed, people can make their own choices. Freedom here is very similar to Kant's view of freedom. But Kant's freedom is rational moral self-discipline. Even if will is free, its foundation lies in reason. Rationality becomes the prescribed basis of human will. Sartre believes that this universal rationality is the essence of the regulations and restrictions on people, which precedes the existence of people. Sartre also showed that his starting point was Descartes' "I think". "I think" is self-awareness and self-existence. This kind of consciousness can be seen. It goes without saying. It deserves to be the most solid starting point of subjective philosophy. Its confirmation is unshakable in Descartes, Husserl and Sartre. Based on "I think", existence is born. At this time, existence is free, because at present, everything is uncertain except existence itself. Existence is discovered before other things. However, if existence is so free and there is no God to bind people. Then, "If God doesn't exist, everything is allowed." At this time, Sartre naturally introduced the concept of responsibility. In western culture, there is a concept that is self-evident. If a rational person is free, then he should take full responsibility for his actions. Sartre believes that this responsibility is unshirkable. He has a concept called self-deception. He believes that self-deception is often an excuse to avoid responsibility. He gave an example of a priest. You have to make a decision, and it is difficult to make up your mind, so you find a priest and get a guide from him. Then even if this guidance brings troubles and difficulties in the future, you can't put the blame on the priest at this moment, because you chose to trust the priest. You are also responsible for this behavior. This paper aims to refute two kinds of accusations against existentialism. One of them is that Christianity believes that people can do all kinds of evil without God. Restricting freedom with the concept of responsibility is an effective rebuttal to this accusation. Loneliness is rooted in Descartes' "I think", and the concept of "I think" will naturally bring a trouble. That is the problem of intersubjectivity. You are thinking, and your existence is self-evident. However, you don't know whether others exist as clearly as you do. That is, the * * * production party (which should be the French * * * production party) is attributed to existentialism. Your existence is so free that nothing seems to stop you. You can choose whatever you want. Isn't this a very strong subjectivity? Sartre's refutation is realized by turning the decision of freedom into action. Although you have chosen what freedom is, you must put it into practice and action, because you are responsible for your free choice. And existence is generated in action, and people constantly improve themselves in practice. To popularize it, we need to refine two concepts first, one is "letting go". In other words, it is ourselves who decide our existence. This obedience is accompanied by pain. "Despair" means that we can only limit all our dependence to remembering our will, or to many possibilities that our actions will work. The popular expression of Sartre's thought is that resignation means that I can make choices freely and plan our lives, but at this moment you are a little hesitant and uneasy. Is this good? This comes from the fear of uncertainty. Because you speak for yourself, it is difficult for you to understand the state of others. Because others also have the freedom to choose, you don't know if others will defect halfway. So you can only rely on yourself. This is a feeling of despair. The choice in doubt is free, only whether to choose or not, there is no question of subjective probability. Sartre seems to have no need to consider how sure it is. Take action. You must bear all the consequences of your action. As long as you are conscious, there is no problem choosing anything. In this paper, Sartre did not provide specific ethical norms, but only put forward his model of freedom and responsibility. In other words, it is generally difficult to distinguish good from evil without human stipulation. Christianity, for example, has clear doctrines and creeds because of the support of God. Kant, reason at least provides morality.