A switching power conversion circuit includes a power circuit, a feedback circuit and a control circuit. The power circuit includes a switching circuit and a first magnetic element. The first magnetic element generates a magnetic flux change by alternately conducting or shutting off the switching circuit, so that an input voltage is converted into the output voltage by the power circuit. The feedback circuit generates a feedback signal according to the output voltage. The control circuit is used for controlling an on duration and an off duration of the switching circuit, thereby maintaining the output voltage at a rated voltage. The off duration of the switching circuit is maintained at a constant interval under control of the control circuit. The on duration of the switching circuit is adjusted to be a specified interval smaller than a maximum on duration according to the magnitude of the input voltage.