Guizhou plateau, a karst plateau mountainous area, locates in the center of southwest China karst. The ecological environment background there is complex with sharp cutting surface, great elevation and steep slope as well as the monsoon climate with perennial cloudy and rainy weather. As a result, the quality of the remote sensing data from the satellite is often affected seriously. This study is taking Sizhai town in Guizhou province as an example and focusing on the fusion with the 4, 3, 2-band multi-spectral and the panchromatic band from IRS-P6 satellite remote sensing images. The four ordinary fusion methods include IHS, PCA, Multiplicative and Brovey transform. Studies show that fusion result of IHS is the best. It not only maintain the spectral information of the original multi-spectral image, but greatly improve the spatial resolution, the visual effects, the expression of clarity and the texture details. As the most suitable fusion method used in sub-tropical karst plateau mountainous region, IHS fusion method can enhance the image resolution greatly and improve the images visual effects and enhance the sharpness and lines detail. So, IHS fusion is of significant to get high-quality images that is difficult to get in sub-tropical karst plateau mountainous region.