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In this paper, a classification-based adaptive compression method for computer screen image is presented. This method firstly divides the computer Screen Image into 16×16 non-overlapping blocks, and then every block is classified into three types: text/graphic, pictorial and hybrid blocks based on the characteristics of histogram distribution and the number of colors. For complex text/graphic block, k-Means clustering method is used to reduce the number of colors to improve compression performance, finally the text/graphic block is coded by our proposed lossless coding method, hybrid block is coded by hybrid coding method and the pictorial block is coded by H.264-like intra coding method. Experiment results show that our proposed block classification method exactly distinguishes three block types, color clustering method can effectively reduce the number of colors for complex text/graphic. The compression performance and subjective image quality of our proposed method can outperform JPEG and JP2k.