In order to achieve high conversion efficiency in a wide load range, a hybrid modulation mode of DC-DC converter was designed, which combined PWM modulation with PSM modulation. A simple self-adaptive modulation switching circuit was designed, and a new synchronous generator circuit of minimum duty cycle signal OSC, VRAMP signal and clock signal VCLK was designed using slope descent edge of ramp generator circuit to simplify the circuit scale. Under light load, the modulation mode was automatically switched into PSM modulation mode by detecting duty ratio and output voltage simultaneously, which reduced the operating frequency of the switching circuit, and the static loss was reduced by 40%. The circuit was designed in a 65 nm CMOS process. The simulation results showed that the circuit could switch smoothly between the two modulation modes, and the working efficiency was improved to 863% at 1 mA load.