The purpose of this study is to improve the efficiency of the single-phase PWM DC-AC inverter based on the optimization of the switching-phase of the PWM. The improvement of the efficiency means to improve the quality of the output waveform, the efficiency of the power conversion, and the reduction of the switching-loss. In order to solve these requirements, we consider the swarm intelligence optimization method to optimize the switching-phase of the PWM. We define an evaluation function and we search the minimum value of the evaluation function by using the swarm intelligence optimization algorithms. In this year, we pay attention to the Differential Evolution algorithm (abbr. DE). DE is one of the most efficient swarm intelligence algorithms. As the result, the DE can reduce high harmonic components in the output signal comparing with the conventional triangle wave comparison method. Also, the result of DE is better than our previous results by using PSO algorithm. We confirm that the DE can improve the quality of the output waveform and the efficiency of the conversion.