Abstract: To meet the needs of open system and specific requirements of CAD platform, the component-software bus model (CSB model) is presented. In this model, graphic functional modules and application modules are encapsulated into components and integrated through software bus. Application components based on interpreted and compiled language work together on the same platform, can be added to and removed from the system at run time. Communication between components together with data format transformation is accomplished by Application Service Interface which is composed of Bus Facilitator, Interpreter and Application Service Agent. Based on this model, we have developed a CAD supporting system named OpenDesign, which has successfully come into the market. The CSB model is proven to be a solid base for CAD supporting system with high efficiency, interoperability, scalability and openness.