Aiming at the problem that the discrete wavelet transform multi-focus image fusion algorithm ignores the low frequency component in fusion processing and leads to edge distortion and image blur. An adaptive region fusion rule of multi-focus image fusion algorithm is proposed. First of all, the source image is decomposed by wavelet, and the low frequency and high frequency coefficients are obtained. Then the threshold processing of low frequency coefficients of the approximate information are carried out with the improved spatial frequency. Then, the improved gradient and the sum-modified-Laplacian high frequency fusion rule are utilized on the representative information. Finally, the processed high frequency and low frequency coefficients are reconstructed by wavelet transform. Experimental results show that the proposed algorithm can preserve the image contour information and edge information subjectively, and the fusion result is better than the traditional fusion methods. The objective indicators are greatly improved objectively.