A simulation of light beam propagation in the misaligned optical system under mechanical vibration is deduced by the means of ray tracing method based on coordinate transformation and reflection law. A telescope structure of an apparatus was constructed which was then imported into Patran_Nastran to perform a transient response after sine vibrations was applied in the xyz directions simultaneously so as to obtain the displacement of key points of mirrors. Then, the displacement was used by the simulation program to compute the jitter angles. The amplitude of beam jitter angles were 0.003 4°, 0.016 1°, 0.017 7° respectively after optical beam reflected by primary mirror, secondary mirror and reflection mirror. Moreover, the traces of facula in the target plane and in the space were drawn.