Abstract: Since 1999, the expansion of colleges enrolment has had a profound impact on the economy and society. Most of the previous literature focused on the impact of the expansion of colleges enrolment on the labor market, lacking of research on the impact of macro-economy, especially on the impact of regional innovation ability. Most of the research on education shows that the expansion of university enrollment in a short period of time improves the level of regional human capital, which will have an long time impact on innovation. Based on this assumption, this paper uses the difference-in-differences (DID) method to test the impact of the enrollment expansion policy on the innovation ability based on quasi nature experiment by using the provincial panel data in 1990-2013. Specifically, by multiplying the number of enrollment expansion in each province over the years with the policy dummy variables before and after enrollment expansion, a continuous DID model is constructed to evaluate the effect of enrollment expansion policies on regional innovation ability. In order to further analyze the educational quantity effect and educational quality effect caused by college enrollment expansion, we replace the processing intensity of college enrollment expansion with educational quantity and educational quality respectively. Among them, the quantity of education is measured by the number of new college students every year, and the quality of education is measured by the ratio of teachers to students. By comparing the two functions, we can identify the impact of college enrollment expansion on the quantity and quality of education.The conclusion of this paper shows that after controlling other factors, the expansion of education quantity increases the innovation ability by 44.22%, and the change of education quality increases the innovation ability by 1.12%. There is interaction effect between education quantity and education quality, and the marginal effect of improving education quality to promote innovation is greater than that of education quantity. After the enrollment expansion, the quantity and quality of education significantly improve the innovation ability, and the quality and quantity of education promote innovation through mutual influence. On the whole, the positive impact of the current expansion of education quantity is more than the promotion of education quality on innovation ability, but most of this effect comes from the improvement of education quality. There is a quality threshold for the effect of quantitative expansion, so improving the quality of education is the key policy aim. The college enrollment expansion policy mainly affects the innovation ability through the way of human capital accumulation. The expansion of education quantity promotes the accumulation of human capital, while the effect of education quality accumulation of human capital is less than that of education quantity, but the effect of education quantity is more from the improvement of quality. Mechanism verification shows that the promotion of human capital is the main way to promote innovation by expanding enrollment (education quantity and education quality), and the role of education quality in promoting human capital is greater than that of education quantity.Compared with the similar research at home and abroad, this paper evaluates the effect of college enrollment expansion from the perspective of innovative production, which is different from the previous literature that evaluates the effect of college enrollment expansion from the perspective of labor market, employment and education yield, and studies the influencing factors of innovation ability from the perspective of human capital investment, economic agglomeration, FDI inflow, innovation environment and interaction between innovation subjects.In terms of theoretical research, this paper analyzes the different effects of enrollment expansion on the accumulation of human capital from the perspective of scale effect and quality effect of college enrollment expansion, which is different from the previous studies on employment and rate of education return. It not only provides theoretical support for the implementation of enrollment expansion policy, but also provides guidance for the promotion of innovation in terms of scale and quality. In terms of research methods, this paper mainly uses the quasi difference-in-differences method to evaluate the role of college enrollment expansion, which not only solves the problem that the national policy cannot construct the experimental group and control group, but also provides convenience for distinguishing the quality and quantity effects. Thus, it solves the endogenous problems in the previous research on the influencing factors of innovation ability, and ensures the credibility of the conclusion of this paper. From the perspective of innovation, this paper evaluates the impact of the enrollment expansion policy of colleges and universities, which provides direct policy guidance for further promoting the enrollment expansion policy of colleges and universities and promoting human capital.This paper holds that the policy of college enrollment expansion is feasible on the whole, but at present, the scale of expansion has exceeded the optimal value, which makes the marginal effect of quantity expansion decrease. Therefore, from the perspective of education development, quantity expansion has its positive significance. On the premise of maintaining a moderate increase in quantity, we need to carefully control the overall rapid increase in quantity. In the case of limited educational resources, blindly increasing the number will only make too few educational resources be apportioned and will not produce the role of accumulating human capital to promote innovation. The core of human capital accumulation in education is to improve the quality of education, while the decline of education quality will only restrain the accumulation of human capital, thus hindering innovation. On the other hand, more reasonable allocation of educational resources. Because of the difference of educational resource allocation and the difference of economic development level, the effect of educational policy will deviate. Therefore, on the basis of balanced allocation of education resources, we should increase the proportion of education funds in GDP, pay more attention to the support for the deficient and backward areas, optimize the efficiency of the use of education resources, improve the quality of education, and thus improve the innovation ability.

Key words: colleges enrolment expansion, education quantity, education quality, innovation ability, difference-in-differences method