Power spectrum of the unsteady wind loads is describes in detail. The linear relationship between rigid displacement of the optical elements and specular node is built by the least squares method. And the optical sensitivity matrix characterizing the optical image point offset caused by a rigid displacement of the optical elements in the optical system is built based on the assumption of small displacement linearization method. Then, these linear relationships are imported into the finite element analysis model of the telescope system and the frequency response analysis of unsteady wind loads is proceeded. The random response curves of image point offset relative to the imaging surface are obtained from input of the power spectral density functions of unsteady wind loads under sixteen cases of different wind speeds and elevation angles. Finally, the random response curve of image point lateral displacement is corrected considering the impact of main axes servo control system and the integration time of imaging elements on image offset. And line spread function (LSF) and modulation transfer function (MTF) attenuation curves caused by the random offset are deduced. The Strehl Ratio of imaging system is calculated in sixteen cases in the short and long exposure time. The results show that the Strehl ratio of the optical system is greater than 0.8, when the telescope is located in fifth level wind under any elevation angle and in sixth and seventh levels wind under near 0° elevation angle. Under the above circumstance, the telescope system can work properly. While the Strehl ratio is less than 0.8, when the telescope is located in eight level wind under any elevation angle. In this case, the image quality of the telescope is seriously affected, so the system cannot work properly.