Whether the active power filter can reach its expecting controlling results according to working theory or not，it depends on control strategy，fast speed as well as the accuracy of harmonic detecting algorithm. It classifies the control strategies of active power filter and analyses deeply the results of common control strategies，summarizes their advantages and disadvantages. Among them，the combined control strategy is an ideal way，because the advantages of detecting load harmonic current controlling method and the power system harmonic controlling method are sumed up.