According to the reliability requirement of the Flight Control Computer for Unmanned Aerial Vehicle (UAV), a design scheme is proposed to ensure its reliability by using tri-redundancy technology. Further, by selecting appropriate redundant mode and the architecture model of the triple redundant flight control computer is established in this paper. The multi-channel security level method can give full play to the error tolerance ability of the system and improve the fault tolerance performance of the aircraft. After an extensive analysis and study of the structure of each module, the hardware circuit and software flow chart of the key technologies, such as redundancy strategy and synchronization method are suggested. A channel selection method based on channel security level is proposed. Combined with the comparison technology between channels, the selection of the optimal safe channel is realized.