Aiming at the fault tolerance problem of microsatellite computers, this paper proposes a fault tolerance scheme based on on-board resource backup. The scheme for the first time takes the component as the backup equipment of the on-board computer, and by assigning the tasks of the on-board computer to the component, the component replaces the faulty on-board computer to accomplish the tasks. The architecture of the fault-tolerant system based on hardware resources is firstly given, and then a task allocation optimization model is established on this basis, and a task allocation method based on greedy algorithm is proposed to realize the minimum completion time allocation of the tasks of the on-board computer. Finally, the effectiveness of the task allocation method is verified by simulation.