Abstract: According to the equivalent circuit model of an optical addressed spatial modulator whose main structure is a-Si:H/Al/FLC, the resolution, response velocity, contrast ratio and gray scale response characteristics were analyzed by Pspice and Matlab. The results indicate that in the condition of certain FLC cell thickness, the resolution of FLC-OASLM can be increased by decreasing the thickness of a-Si:H, but it makes the dynamic range decrease and manufacture more difficult at the same time; the max MTF value is 1 only when the spatial frequency is 0. The output light is very weak when no write light; when write light intensity is from 0.08 mW/cm2 to 10 mW/cm2, the delay time decreases 110 s and the rise time decreases 154 s; when write light intensity is 1 mW/cm2 and erase light intensity is from 0 to 1 mW/cm2, the delay time increases 41 s and rise time only increases 3 s; so the response velocity of FLC-OASLM can be increased by increasing the intensity of write light or decreasing the intensity of erase light in the conditions of certain other parameters. The contrast ratio of FLC-OASLM increases slowly at a low control light intensity, but it increases quickly with the further increasing control light intensity, and finally it is close to a steady value which is 21:1 in this paper. In the conditions of certain other parameters, the response of output light falls step by step with the increasing intensity of erase light; and after erase light intensity arrives at 3 mW/cm2, the changes of erase light intensity have nearly no effects on the rise time; while the fall time keeps on decreasing with the increasing erase light intensity; more than ten gray scales can be obtained by designing the drive source signal reasonably; so these indicate erase light can realize gray scale function of FLC-OASLM. Simulation results agree with the tested results from others-essays well. The excellent performances make FLC-OASLM have a wide application in the fields of optical information processing and optical imaging.