Abstract: This paper introduced the importance of diagnosing, preventing and controlling forest diseases and insect pests, and the meaning of building this expert consulting system. It analyzed the process for the forest protection experts to diagnose forest diseases, the composition of knowledge, and the indicating methods of diagnosing knowledge of the forest diseases and pests in the expert consulting system. We designed the structure, knowledge base and inference mechanism of the expert consulting system. Inference mechanism and problem solving process were given and the expert consulting system was developed based on web for the diagnosis, prevention and control of important forest diseases and insect pests. The system consists of four main subsystems, ie the subsystems of knowledge base management, the forest diseases and pests index, forest diseases and pests diagnosis and the prevention and control pesticide information of forest diseases and pests. The system is released on the Internet through ASP, which can be operated from long-distance. Using this system will prominently enhance the management of prevention and control of the forest diseases and insect pests.