Abstract: The paper analyzed error cause by ues of traditional p-q detection method to detect harmonic current,reactive current and negative current of load current,and proposed an improved p-q detection method. The improved p-q method makes use of one-phase voltage to construct virtual and symmetrical three-phase voltage to replace real three-phase voltage,it can detect harmonic current,reactive current and negative current when voltages of power network is asymmetric,so as to eliminate error of compensation current detection caused by asymmetric cause.The simulation result validated the detection method.