8x8 transform has been introduced in H.264's high profile to improve the video quality. After transform and quantization, if all the coefficients of the block's residue data become zero, this block is called all-zero block (AZB). Many 4x4 transform AZB early detection algorithms have been proposed to skip transform and quantization process. In this paper, after theoretical analysis performed for the sufficient condition of 8x8 AZB detection, sum of absolute differences(SAD) and sum of absolute transformed(SATD) based 8 x 8 AZB detection algorithms are proposed. Experimental results show that the proposed algorithms achieve major improvement of computation reduction from 0.95% to 79.48% for 720p sequences. The computation reduction increases as QP increases.