The shock of higher education expansion is beyond the labor market, and its effect oncollege graduates' happiness should be evaluated comprehensively from a broader perspective. Based on China General Social Survey and a conceptual framework of "local average trestment effect", this paper identifies different groups whose education achievements are affected by higher education expansion heterogeneously, and examines the heterogeneous treatment effect of higher education expansion on graduates' happiness quantitatively by difference-in-difference method. It comes to the conclusions as follows:firstly, a sharp increase in the scale of college enrollment deteriorates the always-takers'happiness because their competitive advantages in the labor, marriage and other markets are weakened; secondly, as for the compliers who benefit from higher education expansion and thereby have the opportunity to receive a college education, their happiness is not improved accordingly owing to a bigger gap between their campus life & graduation prospects and their imagination. In the transition period of higher education development from the number expansion stage to the quality upgrading stage, this paper provides a reference for the families to invest in education from a perspective of subjective welfare, and also the decision-making basis for the government departments to deal with the negative impact of higher education expansion.