An application of Rough sets theory in target recognition system is researched based on data fusion of the multi-spectrum images. The method of expressing the information of the target is introduced, and the idea of dispersing the continued data by using the C-means method is presented. By reducing the decision-making table, targets recognition are realized . It is used to recognize the target from the light, middle and long wavelength infrared images in this paper. Experimental results prove that this approach is good for the target recognition and can easily get the pre-knowledge.