Abstract: It is not uncommon that some relays of the spacecraft would fail due to the contact accretion. The inrush current, caused by the capacitive load, will appear when the relay is closed, although the derating design takes account of it. The inrush current may melt and erode the contacts to present potential risks of the failure of the relay. In this paper, the erosion of the relay contacts by the inrush current is studied, the capability of standing against the inrush current of the spacecraft relay is tested, the mechanisms of the contact erosion and welding are analyzed, tp give guidance for the proper use of the spacecraft relay and to improve the reliability and safety of the spacecraft relay usage.