The a-Si:H thin film is used for a photosensor in liquid crystal light valve(LCLV). A lumped element model for the layered a-Si:H LCLV is developed. It has been shown that the dark and photo-resistances of the a-Si:H photosensor should be adjusted respectively to within the region between one order of magnitude higher and one order of magnitude lower than that of the liquid crystal(LC) layer to ensure a linear variation of the voltage across the LC with the intensity of the incident write-light beam. For obtaining an optimal operation condition of the LCLV, we can determine the concrete values of the dark resistance of the photosensor from the threshold voltage of the LCLV for the linear change of the LCLVs grey level and the applied voltage of the LCLV, and the photoresistance of the photosensor from the saturation voltage of the LC. As a result, the application of an a-Si:H film by optimization of the deposition condition indicates that the contrast of LCLV can be improved distinctively.