In order to obtain better fusion images,an improved algorithm on the basis of structural similarity ( SSIM) threshold is proposed to determine fusion rules adaptively.In the algorithm,for low frequency sub-bands,a weighting summation fusion algorithm on the basis of correlation coefficient and deviation from mean is adopted to preserve more general information.For high frequency sub-bands,the SSIM of each region of the image to be fused is calculated first and then the corresponding average value is taken as the threshold.Afterwards,a high frequency subband fusion algorithm is selected adaptively according to the relationship between the SSIM of each region and the threshold,so as to retain more detail information.Experimental results show that the improved image fusion algorithm helps achieve the fused images of richer detail,sharper edge and better objective evaluation index of quality.