An improved detection method for observing the zero quantized block (ZQB) is proposed. The additional computational cost would be reduced due to 4 x 4 ZQBs being detected prior to the 4 x 4 DCT forward transform and the quantization processes on H.264/AVC video coder, we report a new criterion based on the statistical analysis by considering the energy conservation theorem. Experiments are also carried out to validate the present method. The results indicate that the present method has both a better detection rate with the negligible PSNR degradation and a reasonable error and/or false detection comparing to the prevalent methods. Particularly, computation savings are obtained as well.