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H.264/AVC is the newest video coding standard with high compression efficiency. Especially it adopts traveling algorithm to find the optimal mode for intra-frame prediction in spatial field, so it is quite complex and costs very long encoding-time. In this paper, the proposed fast mode decision scheme consists of two parts: early intra mode detection, which is to select intra 4 × 4 or intra 16 × 16 mode for each MB before encoding according to smoothness characteristic, and fast intra4 × 4 mode decision, which is to reduce choices of prediction directions from 9 to 3 by SAD of Mode 0 to Mode 2. Experimental results show that without the variety of PSNR basically, the compression time is 32.8% less than the original algorithm, and only increases 3.2% bits-rate on average. This algorithm improves the intra-frame coding efficiency, and is especially applicable for the high quality and complex sequence.