Abstract: Aimming at the improvement of radiation resolution in new generation remote sensing images,a method that used for computing double byte joint entropy is provided.At the same time,some further questions,such as how the quantitative series affect the entropy,what kind of method can be used to reduce the correlation of pixels and different bands in multispectral image and how to compute and analyse joint entropy for images which is close to non-memory for more accurate result,are discussed.The developing method can be used for the optimum bands selecting and quality evaluation in image fusion.