Modulation transfer function is a common method for evaluating the performance of optical imaging system. The measurement of MTF is very important in production and testing. But there is no standard quantitative method for the measurement of projection lens in the production of projection display system. A new method of measuring LCD projection lens' MTF with CCD imaging system placed on the image plane is introduced. The method is based on the theory of Fourier transform and linear system, and can provide a quantified standard for lens measurement. At the end, the testing results of some practical objective lenses are presented and compared with the designed MTF. Factors that will affect system accuracy are also analyzed here.