An expert system was developed to diagnose the fault in lehr of float glass production line.The time-lagging problems of diagnosing fault and their relevant solving method for lehr can be efficiently solved by this system.Visual(C ) was used to enhance the friendship of the program's interface,which was convenient for the user to master this software in a short time.In addition,the case-based reasoning(CBR) is used in this expert system,which can enhance the conclusion reliability and the running speed of the software.