A switching power conversion circuit includes a conversion capacitor, a capacitive power conversion circuit, an inductor, an inductive power conversion circuit and a switching control circuit. The capacitive power conversion circuit switches the conversion capacitor periodically according to a switching control signal generated by the switching control circuit, to generate a first intermediate voltage and a first proportional voltage in a promptly rising mode and to generate a second intermediate voltage and a second proportional voltage in a promptly falling mode. In the promptly rising mode, a rising slope of an inductor current is determined by a difference between a high level of the first proportional voltage and an output voltage. In the promptly falling mode, a falling slope of the inductor current is determined by a difference between a low level of the second proportional voltage and the output voltage.