The general optimization design method, such as Simplex method and Powell method, etc., can determine the final optimum structure and electric parameters of an electron optical system from given electron optical properties, but it may land in a local minimum of the optimum search process. The Genetic Algorithms (GAs) is a novel direct search optimization method based on principles of natural selection and "survival of the fittest" from natural evolution. Through the "reproduction", "crossover" and "mutation" iterative process, GAs can search the global optimum result. In this paper, we applied the GAs to optimize an electron emission system, a "triode" structure used in a projection display with high resolution and brightness. The optimal structure and corresponding electrical parameters with a criterion of minimum objective function value, crossover radius, have been searched and presented in this paper. The GAs, as a direct search method and an adaptive search technique, has significant advantage in the optimization design of electron optical systems.