The rapid development of electronic products today, it is a very important part of that electric shock prevention remains the safety design of electronic products. When unplug the electrical equipment, the voltage in each pin of the plug is residual voltage. If residual voltage is too large, it may cause harm to human body, must attach importance to it and precisely measure it. Load of different electrical products lead to different transient voltage changes in sudden power-down, namely the changes in the residual voltage. In this paper, the load on the electrical equipment on the basis of type classification, focusing on the design of their corresponding capacitive load and peak power detection circuit link was simulated, thus arrive at the variation discipline of residual voltage, in order to better protect human safety.