Abstract The expressing method of synthesis knowledge by frame plus rule and neural network plus mathematics model is presented. Through corresponding transform,the expressing method will become reasoning rule. According to the possible modes of stabilization of gangue dam slope,the hardness degree of rock,joined state and development degree of structure surface,the character of flabbiness surface of dam bed,the fragmentation state of dam shoulder and seepage are considered. The illation and evaluation on the stability of the 2nd gangue dam in Dexing copper mine are made.