By analyzing the traditional FBD harmonic detection method,improvements have been made in the shortcomings of obtaining reference voltage references and fundamental currents.At first,a reference voltage detection method using voltage series to decompose and replace phase-locked loop is designed to obtain a reference voltage with the same frequency and same phase as the fundamental positive sequence voltage;At the same time,replacing low-pass filter with LMS self-adaptive filter and adding a closed loop so that the detected harmonic current feedback to the input current.The improved filtering method can significantly improve the tracking speed and dynamic performance.Finally, the correctness and superiority of the improved FBD harmonic detection method are verified through simulation experiment.