This paper presents a method that applies XML technology to structure the design process data of products. The design process data includes product data, process data and process management data. Applying XML technology can build a structural and platform-independent Design Data Model (DDM), and make it possible to reuse design data in the life cycle of a product. DDM is based on a Process-based CAD (PCAD) model and a software prototype based on PCAD has been developed using Java and XML technologies that are platform independent. A Document Object Model (DOM) technology is used to operate XML documents and an example is presented to demonstrate this method.