Detecting harmonic and reactive currents accurately is one of the key technologies which influence the compensation performance of active power filter. Aiming at the shortcomings of traditional FBD method in detecting harmonic and reactive currents, an improved FBD detection method without phase-locked loop is proposed in this paper. This method uses the fundamental positive sequence voltage extracting segment instead of phase-locked loop, to get three-phase reference voltage signals having the same frequency and phase with the fundamental positive sequence voltage, by processing two line voltages, and then to obtain the compensation command currents. The detection result is not affected by the asymmetry and distortion of the grid voltage, and eliminates the error from phase-locked loop. Simulation analysis and experimental results verify the correctness and feasibility of this method.