Low orbit low-cost commercial satellites often adopt dual OBC (On Board Computer) design based on CTOS(Commercial-Off-The-Shelf) devices, if the main OBC falls in failure, the backup OBC will take effect, making the whole satellite system stable. Aiming at the requirements of reliable arbitration and task parameters recovery, a special warm-stand-by system is designed compared with existing cold/hot standby solution, based on TRM(Triple Modular Redundancy) principle. Three simple MCUs(Microcontroller Units) are used as intelligentSjudgmentSunits, it can switch active OBC according to ground commands, or take automatic execution based on embedded algorithm by real-time monitoring of the operating parameters of the working OBC; Then recover the system key parameters and task data by the periodic copy of three MCUs, to make continuity of onboard missions. The verification results show that after fault injection, the dual OBC arbitration system is acurrate and onboard missions are continuous, improving the reliability and fault tolerance of the system.