Regarding to the issue of how Electronic Reconnaissance Satellites(ERS) execute the regional survey mission task, the optimization model considering time, area and frequency are established by analyzing the application scenes, task requirements and the constrained conditions of ERS, through dividing the observation area into grids, the discretization of the observatory time, and the processing on the observatory frequency. The genetic algorithm could apply to the model by modifying the structure of code, initializing the method and introducing the penalty function. Conclusion of the simulation indicates that the ERS area census task could be effectively executed with the proposed model and algorithm.