A photorefractive joint transform correlator(JTC) based on the nonlinear transforming ability of liguid crystal light valve(LCLV) is presented.The real time image differentiating and image grayscale reverse is performed with the nonlinear transforming ability of LCLV only by changing its biasing voltage.Joint transform spectrum is recorded by photorefractive crystal LiNbO 3.The JTC of positive,differential and grayscale reverse image of an input scene can be real time performed using the JTC.Computer simulative and experimental results of JTC using different input scene are given and analyzed.