In this paper，a common global model and system of condition monitoring and decision has been presented for the flexible manufacturing system on the basis of the characteristics of FMS devices and processes and the requirements for monitoring and diagnosis. This system is composed of several subsystems of distributed multi-sensor，feature extraction, condition expression and classification，global comprehensive decision on fault. Its aims are to try to solve the question of the real-time and in-time monitoring. The practical systems bui1t on the flexible machining systems indicate this model and system is efficient.