As the inspection demands of the transmission, it is necessary to enhance the efficiency of power inspection. Taking all factors which have significant effects on the running status of the transmission lines into consideration, this system establishes a state prediction model of transmission line based on rough set theory and decision tree. The rules which extract from the model apply in the abnormity prediction of the transmission lines. The manager can work out a scientific and reasonable inspection plan in accordance with these rules. This model is proven and have a higher accuracy.