In order to improve the error-correction performance of polar codes with the medium and short code length, an improved decoding algorithm of successive cancellation list of polar codes based on error set (ES-SCL) is proposed. The algorithm first constructed an error set according to the channel characteristics of polar codes. Then the parity check (PC) bits were set according to the elements in the error set during the encoding of polar codes and the information bits and frozen bits were placed in the remaining positions. When the decoder decoded the PC bits, each path did not perform the path splitting and pruning, but could get the estimation of the PC bits through the check function. For the other bits, the decoder would directly perform the SCL decoding. Simulation results show that under the additive white Gaussian noise channel, when the code length is 512, the code rate is 0.5, the block error rate is 10-5 and the maximum list length is 8, compared with the PC-PSCL and CA-SCL decoding algorithm, the proposed ES-SCL decoding algorithm can achieve a gain of about 0.18 and 0.15dB. When the code length is 256, the code rate is 0.5, the block error rate is 10-5 and the maximum list length is 8, compared with the CA-SCL and PC-PSCL decoding algorithm, the proposed ES-SCL decoding algorithm can achieve a gain of about 0.3 and 0.35dB. Furthermore, the ES-SCL decoding algorithm that uses the partial bit splitting decoding can reduce the sorting number of about 50% when the block error rate is almost the same as that of the PC-PSCL decoding algorithm, thus its decoding complexity is lower.