Market access regulation is a necessary means to enhance the supply efficiency of education products. Thus, this paper builds a mixed oligopolistic market of a public school and several private schools, examines the impact of access regulation (i.e. the number of schools) on social welfare, and investigates the roles of the operating cost of schools with different natures and the externalities of education products. The research reveals the great boost of access regulation to the social welfare of the education market and the dependency of access regulation on both the operating cost of schools with different natures and the externalities of education products. Under the premise of fairness and efficiency, the government should establish a scientific market access standard, raise the threshold for market entry and prevent the disordered competition according to the externalities of different educational fields.