Abstract: In view of problem that common ip-iq harmonic current detection method cannot consider filtering effect and real-time performance simultaneously because of using digital low-pass filter, the paper put forward a kind of improved method using mathematical morphological filter to instead of digital low-pass filter. Through selecting proper structure elements, a low-pass morphological filter was designed combining with basic morphological operations. The simulation results showed that the real-time performance of improved method is better than the one of common harmonic detection method under ensuring detection accuracy, which has certain reference and practical value.