Abstract: According to the wavelet transform theory, several groups of multi-spectral images were decomposed 1~5 layers respectively by using Db9 wavelet function;and then under the principle of inverse wavelet transform, fused images were obtained.Finally, the image quality evaluation methods such as information entropy, standard deviation, mutual information, and image fusion quality assessment were used to evaluate the fused images under different decomposition layers.Experimental results show that one layer of wavelet decomposition owns the best results in image fusion.