A switching power supply with a quick transient response is provided. A hysteretic control loop which comprises a hysteretic controller (117) and a control signal gate (116) is added to the original PWM control loop of the switching power supply. The hysteretic controller (117) is used to detect an output voltage (Vout) of the switching power supply and compare the output voltage (Vout) of the switching power supply with a reference voltage (Vref). When a load current (Iout) of the switching power supply is suddenly changed, the output voltage (Vout) of the switching power supply fluctuates. If the output voltage (Vout) of the switching power supply is in a setting range of the hysteretic voltage, output terminals (SELp, SELn) of the hysteretic controller (117) are in a low potential, and the control signal gate (116) selects output signals (Qp1, Qn1) from a PWM controller (101) as input signals of a gate signal drive circuit (106). If the fluctuation of the output voltage (Vout) of the switching power supply exceeds the setting range of the hysteretic voltage, an output terminal (SELp, SELn) of the hysteretic controller (117) outputs a high potential, and the control signal gate (116) selects output signals (Qp2, Qn2) of the hysteretic controller (117) as input signals of the gate signal drive circuit (106), so the operation of switching tubes (111, 112) at the power lever (102) of the switching power supply is controlled to stabilize the output voltage (Vout).