To make the application of the harmonic current detection circuit structure to three-phase four-wire power system more simple ,the response faster and the test results more accu-rate ,the harmonic current detection method was improved on the basis of instantaneous reactive power theory .First ,we removed the phase-locked loop PLL ,and set a fixed angular velocity and structure of sine and cosine loop ;Second ,we improved the algorithm by proposing a new algo-rithm to remove the zero-sequence component , making the calculations of current positive se-quence component in three-phase four-wire power system easier ;Finally ,we replaced the low-pass filter LPF with notch filter ,filtered the current of 50 Hz frequence out using its point stop filter characteristics ,then compared with the current with harmonic arrent ,measuring the har-monic current quickly and accurately .The simulation proved that the improved detection method made the circuit simpler ,response faster and the test results