Abstract: In this paper,an expert system based on fuzzy classing analysis is proposed,aimed at the measurement and control problem on acumulated errors in the automatic metalcutting line,which couldn't be solved for long.The algorithms of getting error data sample and subordinate function are given.An object property model and a system relationship model are investigated,then the definitions are given.Based on these,a system structure is given and its control principle is explained.A simulation example proves that without adding any hardware,a routine system will be changed from open loop to close loop with it is added this software system and the production line will work precisely for long.That is,life-span of accuracy of this class of the production line will be lengthened very much.