A blind separation algorithm based on blur detection is proposed for a type of permuted alias image with blur difference. In the model of permuted alias image, space domain is selected as characteristic domain. Difference images are obtained by implementing four-phase-difference method, followed by partitioned into sub-blocks to compute variance value of them. Blurry images are separated from the permuted alias image by detecting the blurry sub-blocks with threshold operation. The simulation results show that blurry images can be effectively separated from the permuted alias image without respect to the location and size of permuting image.