1. Degree level and academic status: A doctor is one of the highest degrees, and a postdoctoral fellow is not a degree, but a working stage.

2. Research field and research direction: The doctoral stage is mainly academic research under the guidance of tutors, and the postdoctoral stage needs in-depth research in new fields or directions.

3. Nature of work and career development: The main work in the postdoctoral stage is to engage in high-level research and publish academic papers, which is not a profession. After completing the postdoctoral stage, some scholars may continue to stay in academia or research institutions to engage in teaching or research.