The latest High Efficiency Video Coding (HEVC) standard offers higher performance than existing video coding standards - up to 50% bit-rate reduction at the equal perceptual quality, but with a significant encoder complexity increase. With regard to intra prediction, a set of 35 intra prediction modes is defined in HEVC to enhance the intra coding performance. However, the high complexity makes it difficult to be applied in real-time applications. To reduce the complexity of intra prediction while maintaining the coding performance, an adaptive fast mode decision algorithm for HEVC intra coding is proposed in this paper, which can efficiently reduce the number of the candidate modes for rate-distortion optimization (RDO) and thus the intra coding time. First, the relation observed between the costs of two candidate modes will be exploited to improve the efficiency of prediction. Second, both the texture consistency of neighborhood and the texture characteristic in current predict unit (PU) will also be considered. Experimental results demonstrate that the proposed algorithm saves 30.12% intra encoding time on average without incurring noticeable performance degradation and outperforms the state-of-the-art fast intra mode decision algorithms by achieving a better RD performance with approximate encoding time saving.