Incremental in-plane bending is a flexible and laborsaving manufacturing technology for short production runs in a variety of sizes and shapes. But the technology parameters are interactive intimately and it is hard to forecast and control the bending radius accurately. Based on the features of incremental in-plane bending and the advantage of expert system dealing with problems, an expert system of incremental in-plane bending by designing knowledge base of representation of creation regulation, reasoning system based on rules and search mechanism and explaining system based on prefabricating text has been researched and developed in this paper. The system, making use of ADO technology, Access database and Visual Basic, develops knowledge base, database and reasoning system. Based on client / server model, the system realizes a seamless link between Visual Basic and Matlab by using ActiveX. The system can perform functions of bending radius forecasting and forming program evaluating and optimizing. It has a friendly interface and it is easy to operate and convenient for maintenance.