From the basic principle of traditional ip-iq method, deduced new extracting algorithm of instruction current for instantaneous voltage vector orientation and the fundamental positive sequence voltage vector orientation. The two methods make full use of three-phase voltage of all information and solve the problem that the PLL could not lock the phase precisely, thus quickly and accurately isolate harmonic current that distortion voltage generated. New extraction algorithm provides a new way for active power filter to realize dynamic harmonic suppression and reactive power compensation and has good application value and development prospect.