There are three kinds of professors in American universities-assistant professors, associate professors and full professors. Young people who want to enter the university professor series generally need not only a doctorate, but many people have to do postdoctoral research for several years before they can be hired as assistant professors. He served as an assistant professor for about 5 years and was promoted to associate professor after strict examination. He served as an associate professor for about five years, and then he was promoted to full professor after strict evaluation. It is not difficult to evaluate associate professors, and it is difficult to evaluate professors, because you should not only have outstanding scientific research achievements, but also be well-known in this field. Famous professors can retain the title of professor after retirement, which is called honorary professor.

In many American universities, associate professors and full professors are tenured professors. The so-called tenured professor system means that once appointed, as long as it does not violate the law and professional ethics, the employment period will automatically continue until retirement (retirement has no mandatory age limit and is completely voluntary), and it will not be assessed by the workload of teaching and scientific research at all stages of the school, and there will be no pressure to be dismissed. At the same time, I also enjoy the lifelong professor allowance issued by the school. This is an important institutional guarantee to ensure academic freedom in the United States. This system can provide a free and relaxed academic environment for professors, without worrying about life and work, so that they can concentrate on academic research and produce more masters. Some promising young scholars with great original research results can be hired as tenured professors at the age of 30.

In addition, American universities will choose the best among the best, and employ very few tenured professors as "university professors" (or translated as "university professors"). Under the existing higher education system in the United States, "university professor" is the title that universities can award to professors with the highest reputation and the best treatment. The winners of "University Professors" not only enjoy high academic prestige at home and abroad, but also cover a wide range of fields. They are qualified to teach in more than one department, and their teaching achievements are recognized as outstanding. In addition, they have made outstanding contributions to the universities, professional fields and communities they serve. For example, on 20 10, Jonathan H. Turner, a world-renowned sociology professor, was hired as a "university professor" by the University of California, Riverside. Therefore, he became the 37th person at the University of California, Riverside since 1960, and the second sociology professor to win this prestigious award.

Unlike many American universities, Harvard has no tenured associate professor. So many other universities, such as Yale University and Princeton University, often take advantage of Harvard's lack of tenured associate professors and use tenured associate professors as bait to recruit associate professors from Harvard.

In China, academicians and senior professors in humanities and social sciences are all lifelong honors, which are quite similar to the "tenured professors" in some American universities. At present, China is planning the retirement and withdrawal system of academicians in order to optimize the layout of disciplines and increase the proportion of young and middle-aged talents. At present, the United States also encourages professors with tenure to retire, and universities have begun to reduce the requirements for professors' tenure, but maintain the mobility and flexibility of their positions with the title of assistant professor.