Abstract: This paper discusses the composition and the functions of conductive adhesives used in spacecraft. The basic properties of the MD-140 conductive adhesive and the changes of its mechanical, thermal, and electrical properties after thermal-cycling and particle irradiation tests are studied. Based on the internal structure of the conductive adhesive, its environmental degradation mechanism is discussed. The results show that after the thermal-cycling test, the mechanical property is improved, the electrical property is weakened, the change of the thermal property is not remarkable; after the particle irradiation test, both of the mechanical and electrical properties are weakened, the change of the thermal property is not remarkable.