To reduce the spectral distortion in IHS fusion, fusion process was analyzed by spectral response function, bias and gains of the CCD sensor based on imaging mechanism, and it was simulated from spectral density to the panchromatic images and multi-spectral image. Condition equation was set up to maintain the spectral properties in IHS image fusion, and a new model of fusion was established based on the simplified process. Furthermore, the least square method was used to determine the relationship between the different spectral response functions in fusion process, and then the required parameters were calculated. Finally, we did experiments by using the true QuikBird image data and compared proposed method with others. Experiments show the proposed algorithm not only enhances the spatial resolution of the images but also maintains spectral characteristics better.