In order to design high-performance switching power supply,choose higher performance power semiconductor devices,improve circuit topology,choose and improve control method of the control circuit,optimizing component’s arrangement layout becomes the inevitable way. In this paper,BUCK DC / DC converter’s basic working principle is proceeded,the main circuit parameters are designed. The application of the non-linear programming technique has been discussed in the BUCK circuit in depth,the optimization model is got,and then the simulation of the circuit using the ORCAD PSPICE software is carried on. The simulation result indicates that the superiority of applying the optimization design is very obvious,and it improves the design quality.