To achieve lightweight network collaborative modeling on the client, this paper designs the collaborative modeling architecture based on B/S structure. Considering the product CAD model information can’t be shared on the network, the XML technology is applied to build the middle model expression format which converts the CAD model to the middle model that can be shared among collaborative clients on the network. To solve the problem that the middle model is too huge to transmit on the limited internet bandwidth, the face representation method based on loops is proposed. With this method, the size of the middle model shared on the network can be reduced greatly. The structure of bidirectional inquiring between the feature information and the geometric element information is established in geometric models, and the problem that how to get modified features, topology relationship and geometric elements after design models have been changed is solved.