Phased rectifier thyristor commutate circuit will bring serious harmonic pollution to electric power system. If connect the ordinary settled single tuning passive filter, the harmonic current may be increased, even bring parallel syntony. In allusion to the harmonic problem of a certain steel factory in ZheJiang province, this paper design a project that connect a series reactor at the high voltage side, and the passive filter is parallel connection at the low voltage side. The passive filter adopt the thyristor switch to dynamic plunge and secede, with no process of transition. The reliability of the device is very good, and the compensate effect is also very well.