Abstract: With the implementation of the new video coding standard H.264, there appeared higher demands in spatial resolution transcoding in H.264. Present here a fast algorithm based on direction in intra frame downsizing in H.264, which can improve the speed of reducing intra-prediction frame resolution. Experiments showed that this algorithm can speed up 23 percent transcoding time in intra-prediction frame in H.264 with slight PSNR degradation. It gives certain improvement in real-time for transcoding and ability of changing in bandwidths.