Abstract: Active power filter plays important role to manage the harmonic currents of distribution network, while the key issue is harmonic current detection algorithm. In order to improve the effectiveness of the harmonic current detection, an adaptive harmonic current detection method is put forward based on QR-RLS algorithm, which can accurately separate the fundamental currents and harmonic currents. In this paper, the simulation circuit is built by PSCAD / EMTDC software to obtain the current data. And the analysis of simulation data and measured data verifies the effectiveness of the algorithm.