Abstract: The transformation of block-based DCT has been widely used in many compression standards, such as JPEG, MPEG and H.26x etc. However, for the case that the compression bit-rate is lower, the blockness effect will obviously happen in compressed images. Though many methods have been proposed for removing block effect, the standard to evaluate their effectiveness has to be required. Aiming at the above issue, this paper proposes a new approach to measure the effectiveness of removing black effect, in which both blockness and blurriness strength ratio (BBSR) are computed for measuring the improvement effect of coding method. The experimental results show that the proposed method is identical to the human's subjective assessment.