A control circuit for bypassing a diode current and a control method are provided; the control circuit includes a main module, a diode-current sensing module, a driving module; the diode-current sensing module is for sensing a current flowing through a main diode to generate a sensing current; the driving module is for generating a driving current proportional to the sensing current to drive a main switching transistor to be turned on; the main module, the diode-current sensing module, the driving module form a negative feedback loop to reduce the current flowing through the main diode to a preset value. The present disclosure solves problems in the related art, such as heat generation caused by large currents flowing through a body diode or flyback diode when the main switching transistor is in an off cycle, and the control circuit being out of control due to large currents introduced into a substrate.