The basic principle of switching power supply transient load and the relationship between the output voltage drop and the control loop were analyzed. Besides, several methods to reduce the output voltage drop were discussed systematically, and the digital nonlinear control aiming at increasing the transient load was proposed. Based on above methods, the effect of loop bandwidth, rectification mode, and nonlinear control on the transient response of the switching power supply were comprehensively evaluated. Finally, a DC-DC converter with fast transient load response was designed by using this nonlinear control. The experimental results showed that the output voltage drop could be reduced by 60%, and the recovery time could be shortened by 30% under a pulse load. The experimental results met the design requirements.