In order to improve the design efficiency of the threshing device，an intelligent design platform for the threshing device of a rice and wheat combine harvester was constructed. Firstly, the structural characteristics and design knowledge of key parts of threshing device were analyzed. The methods and technologies of collecting, classifying, sorting and expressing design knowledge were studied. The design knowledge of key parts of threshing device was collected, and the design knowledge of key parts of threshing device was expressed by production and framework knowledge representation. The method and technology of using SQL Server 2012 relational database to store the design knowledge of threshing device were discussed, the design knowledge base was constructed, and Visual Studio 2012 was used as the development tool to realize the functions of knowledge query, addition and deletion by using ADO.NET technology, and the knowledge base management system of combine threshing device was established. Secondly, according to the different structural characteristics of the key parts of threshing device, different parametric modeling methods were studied, Visual Studio 2012 was used as programming software combined with C++ and KF (knowledge fusion) two development languages to secondary development NX software, through extracting the relevant parameters in the design process of threshing device parts, the parametric model library of threshing device was established in NX software. Thirdly, according to the design process of threshing device and the design requirements of parts, the reasoning process of intelligent design of threshing device of rice and wheat combine harvester was studied by using casebased and rulebased forward deductive reasoning method. Based on the analysis of threshing device performance evaluation standards and influence factors, the intelligent design reasoning engine of ricewheat combine threshing device was constructed. Finally, using Visual Studio 2012 as the development platform, combining with SQL Server 2012 database and NX threedimensional software and other tools, integrating knowledge base, reasoning engine, parametric model base and humancomputer interaction interface, the intelligent design platform for threshing device of rice wheat combine was constructed. The intelligent design of threshing device was realized, the utilization rate of design knowledge was improved, the design cycle was shortened, the design cost was reduced, the product quality was improved, and the total agricultural machinery design level in China was improved. 