The state-of-the-art soft-output decoder of polar codes is the soft cancellation (SCAN) decoding algorithm,which performs well at the cost of plentiful computations.Based on the SCAN decoding algorithm,a modified method with revised iterative formula is proposed,marked modified min-sum SCAN (MMS-SCAN).The proposed algorithm simplifies the update formula of nodes and reduces the complexity of iterative decoding process by the piecewise approximation function.Meanwhile,the bit error rate (BER) of the proposed method can approach the performance of original SCAN decoding method without performance loss.The simulation reveals that the MMS-SCAN decoding algorithm can achieve the effect that the BER curve almost coincides with the original SCAN decoding curve.