With the widely implement of nonlinear load,the damage of harmonic on power grid is increasingly serious.Meanwhile, gird-connected inverter is becoming popular.Using its’ surplus capacity is effective to solve the problem of the power quality.This method has great practical values in engineering application. Nevertheless, because of the location of installation and the mode of connection,it’s hard for PV inverter to sample system current or load current, which is essential to improve the power quality.So this paper raises a solution to suppress harmonic of the power system without the gird-side current transformer.The specific frequency and waveform harmonic current is injected to estimate grid impedance.Then the grid-side harmonic current can be estimated based on the grid impedance and the system’s harmonic voltage.Meanwhile, the grid harmonic current can be compensated by closed-loop control.Results of digital simulation show that the proposed method is effective.