Wu Xiaogang and Li Xiaoguang wrote in the second issue of Social Sciences in China for that "employment difficulty" in the labor market is becoming a realistic and urgent problem. With the global expansion of education in the past half century, the problem of education matching (especially the problem of over-education) has appeared in the labor market of different countries. The results show that: firstly, with the upgrading of China's vocational structure, over education shows a downward trend (period effect). Secondly, with the popularization of compulsory education and the expansion of higher education, over education shows a rapid upward trend (generation effect) with the birth generation. Finally, once there is a mismatch between the individual education and the jobs offered by the labor market, it will become a long-term phenomenon in the individual career. These findings have important theoretical value and policy implications for vigorously promoting education power, building an education system coordinated with high-quality development, strengthening the connection and matching between education and labor market, and realizing "making the best use of talents".