Abstract: For avoiding failure, some methods should be adopted before the thermal vacuum test to reduce the outgassing of nonmetallic materials and the related molecular contaminations. This paper analyses the volatilization and condensation characteristics of nonmetallic materials, and the engineering practice of vacuum backout for satellite, then proposes a vacuum bakeout scheme for the satellite, including the profile, the temperature, the time and the pressure of the test. The testing result of a satellite indicates that the scheme is feasible in that it can improve the pressure within the satellite and reduce the possible molecular contamination. After the vacuum bakeout, the failure of the equipment due to low-pressure discharging or molecular contamination can be basically avoided.