In view of the limited depth of field of the image acquisition sensor, which leads to the out-of-focus phenomenon in the local area of the acquired image, this paper proposes a new multi-focus image fusion algorithm. Under the framework of NSST, the fusion rules based on discrete cosine transform (DCT) and local spatial frequency (LSF) are used for the low-frequency sub-band decomposition coefficients, and the fusion rules based on the maximum and minimum filtering combined with average filtering and median filtering (MMAM) are used for the high-frequency sub-band decomposition coefficients; and then perform INSST reconstruction to obtain fused images. The experimental results show that, compared with the classical image fusion algorithm, the proposed algorithm can effectively fuse the high and low frequency sub-band information of the image, and achieves better results in both subjective and objective evaluation.