Abstract: This paper expatiated the Principle of ball bearing lubricated by chlorphenyl silicone oil , and frictional torque of ball bearing can be studied under different vacuum levels or rotational speeds . under 3 x 10 -5 Pa, , engineering tests were conducted on the model machine motor of optical modulator on FY-3 satellite Ultraviolet Ozone Vertical Probe and import motor for eight months . The working contact zones of ball bearings were analyzed by using high power microscope , and the leakage rate of chlorphenyl Silicone oil were all analyzed . The friction of bearing tested tended to be stable as the rotating speed increased . The variation of friction torque of bearing lubricated by chlorphenyl silicone oil was 9 . 8 x 10 - 4 N . m , which was lower than that of motor lubricated by MaPlub 101grease . The leakage rate of chlorpheny silicone oil was 1 . 92 mg . It was concluded that chlorpheny silicone oil can Provide long - term lubrication of space optical modulator