EXPRESS-to-XML mapping is an indispensable foundation in manufacturing network data transmission and share. Put forward and construct a networked manufacturing system with synergy based on the whole life manufacture cycle of the products and the manufacturing information share. Stress is on the mapping mechanism from the standard description language of STEP_NC——EXPRESS to XML，presenting the separate-mapping method with which according to the function and feature of the information to be transmitted and shared, the physical file of STEP_NC is divided into general information structure elements, feature information structure, and operating information structure, realizing the optimally comprehensive mapping with the early binding and the late binding. Build up STEP_XML conversion system. Example is given for component with a hole in running the separate mapping method on the STEP - NC Machine simulation platform. It has been shown that the conversion system and the separate-mapping method are practical and efficient.