The invention discloses a mixed control circuit of a DVS system switch DC-DC converter and a control method of the mixed control circuit of the DVS system switch DC-DC converter. Orderly switching between two control modes is achieved through a mixed digital algorithm based on traditional linear digital PID and nonlinear digital sliding-mode control. In the steady state, a slow loop of a digital PID compensator is selected through the mixed control algorithm to work, and small ripple waves of the output voltage and fast responses to small jumping are achieved. When feedback signals of a DVS algorithm module jump, the loop is compensated by the PID through the mixed control algorithm to stop working, a digital sliding-mode control fast loop is selected, and the DC-DC converter fast gets into the steady state. By means of the mixed control circuit and the control method, the mixed digital control obviously has the high dynamic response speed, and the large the voltage jump amplitude is, the remarkable the advantages are compared with traditional digital PID control. In this way, the mixed digital control DC-DC converter is suitable for DVS systems.