Abstract: The structure parameters of control plunger in an electronically controlled injector were designed and optimized to increase the hydraulic response speed of electronically controlled injector. Based on the analysis of work principle and function of control plunger, a design method of control plunger in the electronically controlled injector was presented. The structure parameters were calculated according to a certain diesel engine. Genetic algorithm was applied to optimize the multi-parameters, an optimum model which uses the injector hydraulic response time as an objective function was presented, and the optimization result was achieved. The performance of injector with optimum structure parameters was approved using the simulation model of electronically controlled injector.