In view of the traditional detection error caused by the use of phase-locked loops in instantaneous reactive power detection， on the basis of the principle of Park transformation， it is proposed to give a fixed value to the angular frequency in the Park transformation matrix， thereby eliminating the phase-locked loop and simplifying the detection circuit. As the response of the traditional low-pass filter is delayed and the filtering effect is poor, the shortcomings of the average filtering method are analyzed， and a method of connecting the improved average filtering module and the low-pass filter in series is proposed. The Matlab/Simulink platform is used to build a simulation model for the circuit detection， and the detection effect is analyzed when the three-phase power grid is unbalanced and distorted. The results show that the use of the improved detection method not only ensures the accuracy of the filtering， but also improves the detection speed and meets the detection requirements of the unified power quality conditioner (UPQC).