For the limitation of the dynamic and time-varying characteristics of the load simulator, a novel design method for the first-order electrical load is presented. By adjusting the turn-on time of switches, the first-order load with the parameters in a certain range can be simulated. The simulation degree of the electrical load might be judged with the area percent of function distance in the load response. For the simulations on three loads with cut-off frequencies as 20，50，80 Hz, the PWM period is 1 ms. The duty cycles are 9.9%,39.4% and 69.1%. The simulation deviations are 1.48%,3.92% and 3.57%. The results show that the first-order electrical load designed with this method can simulate any first-order load with the parameters in a certain range .