Abstract: The paper introduced traditional detection algorithm of harmonic current of ip－iq based on instantaneous reactive power theory. In view of time delay caused by harmonic current detection link, it put forward a new algorithm of real-time detection of harmonic current through adding pre-compensation angles to eliminate time delay based on traditional instantaneous reactive power theory. The dynamic simulation result of Matlab proved that the new algorithm has good compensation effect, which makes the compensated current waveform close to sine wave and realizes real-time detection of harmonic. The simulation results also showed feasibility and effectiveness of the new algorithm.