In order to get the harmonic current in the power system quickly and accurately, an improved harmonic current detection algorithm is proposed in this paper based on the traditional ipiq harmonic current detection algorithm. The improved method proposed in this paper is taking the load side of the threephase voltage through the Clark transformation and Park transformation to produce synchronous spin signal to complete the common phaselocked loop structure of the phase detector function, resulting in phase difference signal Δθ, and then through the PI controller adjustment and integration link to get Aphase base wave electrical angle, and then through the positive and cosine signal generator to produce standard positive and cosine signals to reduce the error caused by voltage distortion;the highpass filter is used instead of the lowpass filter in the traditional algorithm to obtain the threephase harmonic current directly, which simplifies the system structure, reduces the delay and improves the real time performance of the system. Simulink simulation results show that the method can detect the harmonic current more accurately and quickly, and improve the realtime performance of harmonic detection.