Multiple lowpass filter (LPF) with fuzzy reasoning was established, and a detecting algorithm based on S. Fryze, F. Buchholz, M. Dpenbrock (FBD) method was proposed for active power filter (APF). Reference voltage was generated by phaselocked loop(PLL), and load current was projected to reference voltage, and then active power fundamental current and reactive power fundamental current could be detected accurately. The multiple LPF composed of two twoorder Butterworth LPFs was developed on the basis of fuzzy control, and the fuzzy controller was designed by taking into account the changing amplitude of load current and the lowest harmonic current. Compared with traditional current detecting algorithms, this new reference current detecting algorithm based on FBD method is much simpler and of higher accuracy and better dynamic performance even under unbalanced voltage circumstance. Theoretical analysis and MATLAB simulation results have proved the validity and effectiveness of the proposed reference current detecting algorithm.