In one embodiment, a control circuit configured to control a switch mode power supply, can include: (i) a compensation signal generating circuit configured to generate a compensation signal according to an error between an output voltage feedback signal and a first reference voltage of the switch mode power supply; (ii) a switching signal generating circuit configured to control a switching operation of a power switching device of the switch mode power supply according to the compensation signal; (iii) a judge circuit configured to determine an operation state of the switch mode power supply according to the output voltage feedback signal; and (iv) a loop gain regulating circuit configured to regulate a loop gain of the control circuit according to the operation state.