Optical property of infrared lead was solved by finite element analysis to make sure that the deformation of optical system under dynamic environment meets imaging requirement. The optic property of infrared lead was analyzed by means of finite element model based on model updating. First, composite material element was created to simulate the connection relation between parts, and then property parameter of composite material element was modified repeatedly to make the result of tested model and calculated model identical. Therefore, correct and effective model finite element was achieved. Finally, the simulation calculation of transient vibration and overload was carried out for the updated finite element model of Infrared lead. Analysis result indicate: mirror face deflection of structure under dynamic environment less than 3″, and mirror face deformation of structure under dynamic environment less than 1 μm. The mirror face deformation and deflection of infrared lead optical system under dynamic environment were within the allowable range, and the optical property of infrared lead meets the imaging requirement.