The principle of minimum action exists as an axiom in physics, that is to say, "based on the self-evident basic facts of human reason, after long-term repeated practice, it does not need to be proved." The English name is: the principle of minimum action, of course, it should be more precisely: the principle of static action. It is the application of variational principle in dynamic system, which can be used to get the motion equation of the system, which will be illustrated by concrete examples later. The appearance of the extreme thought of the principle of minimum action in the principle of minimum action has profound scientific and philosophical connotations: the source of the thought of the principle of minimum action, various extreme thoughts from life and various extreme phenomena in nature. Generally speaking, for example, a suspended chain with fixed ends has the lowest center of gravity when it hangs naturally; When the thermodynamic system is in equilibrium, the entropy value is the maximum; The water droplets remain as spherical as possible. In weightless air, water droplets can remain perfectly spherical, because objects with the same volume have the smallest spherical surface area, and so on. All the above phenomena show that the creator seems to be a shrewd economist. He always tries his best to design the laws of physics to minimize the "cost". A long time ago, people thought that these extreme problems were just accidental results of some physical laws, but with the development of theory, people seem to gradually realize that extreme value is the most essential law in the universe. Today, physicists have found a principle to describe these extreme problems in a unified form and precise mathematics-the principle of minimum action.