A kind of pseudo rate modulator with two-time-constant is designed. The basic working principle is analyzed and the pulse time and describing function are provided. An improved particle swarm optimization algorithm is proposed with several modulator parameters. A quadratic exponent function is designed for the nonlinear dynamic inertia weight. And the distance between particle and the global optima is introduced. Thus the inertia weight changes with the number of iterations as well as the distance from the global optima. The optimal state of time and fuel are combined and the fitness function is scheduled as the function of time and the fuel consuming. Finally, simulation verifies the effectiveness of the improved constructure of the pseudo rate modulator and the parameter-optimizing algorithm.