Doctoral students should not only publish a certain number of papers in authoritative academic journals, but also produce convincing original research results. Due to the flexible academic system, many students need five or six years to get their degrees.

The academic system of doctoral degrees in American universities is generally 4-7 years, with an average graduation time of 5 years and a long period. Due to the long period of experiments and projects in some majors, the graduation time will be further extended.