A method for improving the conversion efficiency of a CCM mode of a flyback resonant switch power supply, comprising: presetting a critical value Tset, calculating a time interval Ttap between adjacent zero points in the current connection time, outputting a shutdown signal at the zero points, and comparing the time interval Ttap with the preset critical value Tset; when Ttap>Tset, controlling the current shutdown time to be less than the shutdown time of the preceding cycle and outputting a start signal; when Ttap=0, controlling the current shutdown time to be greater than the shutdown time of the preceding cycle and outputting a start signal; and when 0