This paper proposes a maximum a posteriori (MAP) based blocking artifact reduction algorithm for discrete cosine transform (DCT) domain distributed video coding,in which the SI and the initial reconstructed Wyner-Ziv (WZ) frame are utilized to further estimate the original WZ frame.Though the MAP estimate improves quality of the artifact region,it also leads to over-smoothness and decreases quality of the non-artifact region.To overcome this problem,a criterion is presented to discriminate the artifact and the non-artifact region in the initial reconstructed WZ flame,and only the artifact region is updated with the MAP estimate.Simulation results show that the proposed algorithm provides obvious improvement in terms of both objective and subjective evaluations.