H.264 is the latest HDTV video compression standard, which provides a significant improvement in coding efficiency at the cost of huge computation complexity. After transform and quantization, if all the coefficients of the block's residue data are zero, this block is called all-zero block (AZB). Provided that an AZB can be detected early, the process of transform and quantization on an AZB can be skipped, which reduces significant redundant computations. In this paper, a theoretical analysis is performed for the sufficient condition for AZB detection. As a result, a partial sum of absolute difference (SAD) based 4 × 4 AZB detection algorithm is derived. And then, a hardware-oriented AZB detection algorithm is proposed by modifying the order of SAD calculation. Furthermore, a quantization parameter (QP) oriented 8 × 8 AZB detection algorithm is proposed according to the AZB's statistical analysis. Experimental results show that the proposed algorithm outperforms the previous methods in all cases and achieves major improvement of computation reduction in the range from 6.7% to 42.3% for 4 × 4 blocks, from 0.24% to 79.48% for 8 × 8 blocks. The computation reduction increases as QP increases.