Small unmanned aircraft for civil and military has a wide range of applications. The design of traditional UAV avionics system is use discrete lines which link one point to another to communicate. It will make the system complexity, and the anti-jamming performance is poor. A new kind of design idea of unpiloted aircraft digital avionics system based on CAN bus is introduced, and this article also made a further study in the avionics systems’ critical subsystems, components and redundant design. The new avionics system, which used bus communication system has many good points, such as strong anti-interference ability, easily extended, simply configuration and so on. The system also has a certain value to promotion.