To solve the problem of information loss and obvious block effect in multi-focus image fusion, a novel multi-focus image fusion method based on image matting technique was proposed. Firstly, the rough focus information of each source image was obtained by focusing measure, all of which was used to generate the trimap of the fusion image, namely, foreground, background and unknown region. Secondly, according to the trimap, the precise focus region of each source image could be gotten by using the image matting. Finally, the obtained focus regions were combined to consist of new foreground and background. And the optimal fusion of the unknown region was conducted on the basis of the foreground and background, which enhanced the correlations between the nearby pixels of the three focusing regions. The experimental results show that compared with the traditional algorithms, the proposed algorithm can acquire higher Mutual Information (MI) and edge preservation on the objective evaluation. For the subjective evaluation, it can be seen that the block effect is obviously suppressed and the visual effect is more excellent. The proposed algorithm can be applied to the object identification and computer vision to obtain optimal fusion result.