Abstract: Four kinds of materials used in the magnetic torquer of spacecraft are tested to evaluate effects of atomic oxygen and vacuum. Mass loss ratio (SAML) and surface topography change of samples are analyzed using a new type of atomic oxygen facility and other instruments. Results show that vacuum exposure can cause mass loss of materials and the values of four tested materials vary by a difference as far as twenty four times, atomic oxygen can change the color of the samples and cause mass losses, and mass loss ratios differ by twenty five times. Results also indicate that silicone can react with atomic oxygen to form a protective coating, which can protect polymers from atomic oxygen erosion.