A switching power converter including an upper-bridge switch, a lower-bridge switch, an impedance circuit, a first control circuit, a second control circuit and a logic circuit is provided. The impedance circuit generates an output voltage and a sensing current according to a conductive state of the upper-bridge switch and the lower-bridge switch. The first control circuit generates a first pulse signal according to the output voltage. The second control circuit has a first mode and a second mode for generating a second pulse signal and a third pulse signal individually. Furthermore, the second control circuit uses different threshold values in different modes to determine whether to switch the mode thereof, so as to form a hysteretic effect in mode switching. The logic circuit controls the upper-bridge switch by the first pulse signal, and controls the lower-bridge switch by the second pulse signal or the third pulse signal.