Aiming at deviation of the traditional dq0 rotating coordinate transformation method with phase-locked loop of UPQC in the detection of three-phase voltage fluctuation, an improved detection method without phase-locked loop for compensation signal of three-phase and three-line is proposed. The method gives the simplified transformation matrix from abc coordinates system to static coordinates system, by calculating the rotation of transformation matrix from coordinates system to dq0 coordinates system instead of acquisition by the PLL, thereby reducing deviation of detection with the PLL. The proposed method is verified by simulation on the platform of Matlab/Simulink software, and the simulation results compared with traditional method show that the dynamic response is improved and performance in terms of detection accuracy is also good.