In order to deal with the problem of the growing of harmonic amount in low-voltage distribution power networks, this paper takes a 315KVA transformer distribution network to design an experimental scheme for retraining the third harmonic amount in a three-phase four-wire system. The scheme can limit the third harmonic under the condition of three-phase four-wire system and measure the impact of the limitation on current, voltage, current distortion rate, active power and distortion power. Experimental results show that limiting the third harmonic current can notably reduce the distortion power of low-voltage distribution power system, thus the electricity quality is improved, but there's no significant power saving effect.