With the wide application of rectifiers, the harmonic content of power grid is increasing. In fact, the multi-pulse rectifier produces lower harmonic content than the lower pulse rectifier. In order to reduce harmonic content from harmonic source in power grid, the multi-pulse rectifier is designed based on the phase-shifting transformer in this paper. First of all, the design method of multi-pulse rectifier is introduced by theoretical analysis. Then, the harmonic mechanism is deduced by the mathematical formula, which explains the harmonic generation process. After that, the correctness and reliability of theory analysis are proved by simulation. Finally, the harmonics of the multi-pulse rectifier are suppressed by filtering branches.