The system of online identification for the workpiece using ultrasonic detection principle is a component of status monitoring and detection in flexible manufacturing system. Flexible production line process is a dynamic process, which is a complex automatic machining system integrated with various of high- tech. The ultrasonic detection technology, communication technology and database technology are used in workpiece recognition. It has great significance for ensuring the normal and efficient operation of FMS to carry out research on inspecti on and monitoring technology and develop FMS inspection and monitoring system.