Abstract: A spacecraft, such as a manned spacecraft, usually has a satellite power distribution system with a control circuit with multi-relay in parallel. The reliability of the spacecraft depends very much on the control circuit's reliability. It is found in this paper that due to the relay's mutual inductance effect, there is an instantaneous current flowing through the relay coil at the start and end points of the typical command circuit structure, which influences the reliability of the circuit. Defects would exist in widely used arc-restraining circuit composed of two diodes in series, or a diode in series with a resistance. An optimized arc-restraining circuit connecting the diode in series with the relay coil is proposed and validated by calculation and experiment. The experimental result indicates that the optimized circuit can effectively improve the reliability of the control circuit, and remedy the defects efficiently.