In this paper, according to unified power quality conditioner (UPQC) parallel side, an algorithm based on a coordinate transformation of discrete Fourier (DFT) sliding window iterative harmonic current detection and a constant frequency hysteresis control algorithm are proposed. The detection and control algorithm can improve the harmonic detection speed, strengthen the harmonic detection synchronicities, real-time good points. Finally through Matlab/Simulink platform is simulated. The condition of the laboratory design a set of small power UPQC device, and successfully applied to the UPQC, simulation and experimental results demonstrate the above test and control algorithm is effective and feasible.