To meet the design requirements of high precision and long life of scanning mechanism for space optical remote sensing instrument,the design of lubrication and sealing based on the method of grease lubrication was completed. Then the important parts of the scanning mechanism were analyzed and optimized by FEM(finite element method),the lightweight structure of the mirror and optimized support structure were obtained. The analysis results show that the RMS of the mirror is better than 13.2 nm in the experiment temperature range(-30~70 ℃);the design of lubrication and sealing is reliable,the leaking quantity in 5 years is less than 3.5 mg;the mass of scanning mechanism is 4.94 kg,the intrinsic frequency of first order is 116.2 Hz. The designed scanning mechanism can meet the application demand of optical remote sensing instrument.