Abstract: Doctoral students' extended term for graduation is a common phenomenon in China's universities, and it easily leads to negative impact. Comparing China's and overseas doctoral students' education period, taking the data of doctoral students' extended graduation during the last five years of Beihang University as example, and by using the quantitative analysis method, the paper analysed the status and reasons of doctoral students' extended term for graduation from aspects of general condition, disciplines distribution and education mode. The result shows that the doctoral students' education period is becoming longer, engineering doctoral students generally have longer education period, and the proportion of entended term of graduation is high among in-service doctoral students. The reasons are complicated and various. Guaranteeing the education quality of doctoral students is the key to resolving the problem.