Abstract: Fusion of high spatial resolution panchromatic (PAN) image and low spatial resolution multiresolution images (MSI) is a hot topic in remote sensing. Beijing-1 microsatellite provides MSI and PAN data with spatial resolutions of 32m and 4m respectively. The data will be used in city planning, disaster monitoring and so on. Spatial information distortion will occur in results when fusing Beijing-1 data because of the low ratio (1:8) between their spatial resolution. To overcome this problem, we design a two dimensional low-pass filter by measuring the modulate transfer function (MTF) of imaging system from the Beijing-1 PAN image, and this filter is used to evaluate the low-resolution information in general image fusion framework (GIF). Experiments show that this MTF-based method is strong in the fusion of remote sensing images. Both visual effect and quantitative indices of the fusion results show its better performance on keeping spatial information than Intensitive-Hue-Saturation (IHS), Brovey Transform (BT) and Gram-Schmidt (GS) fusion methods. And a good tradeoff between spatial information and spectral information can be obtained by this MTF-based fusion method.