A circuit for controlling a switching mode power supply having a power switch, having: a feedback pulse circuit, configured to receive a feedback signal, and to provide a feedback pulse signal; a load determining circuit, configured to receive the feedback signal, and to provide a load determining signal; a light load pulse circuit, configured to receive the load determining signal and a frequency regulating signal, and to provide a light load pulse signal; a frequency regulating circuit, configured to receive the load determining signal, the light load pulse signal and a normal load pulse signal, and to provide the frequency regulating signal; and a selecting circuit, configured to receive the load determining signal, the feedback pulse signal and the light load pulse signal, and to provide an on control signal and the normal load pulse signal; wherein the on control signal controls an on operation of the power switch.