A new method to calculate the current reference for shunt active power filter (APF) is presented. The fundamental positive component of the supply voltage is obtained by given the sine and cosine table whose frequency is the same as the supply voltage fundamental positive component, generate the current reference with the synchronous detection method. The method obviates the phase-locked loop circuit, avoid the problem of the detection error and delay of the phase-locked loop circuit，the detection accuracy is improved; The proposed method works well under various load conditions, especially in the case of a distorted and asymmetric supply. The theoretical analysis and simulation results verify the validity and feasibility of the proposed method.