Diffraction grating experiment is a basic optical experiment in university physics, which can be used to measure grating constant, wavelength of light and other physical quantities. In this paper, the projector LCD screen is used to replace the grating in the diffraction grating experiment, by designing a series of gradient grating pictures and displaying them on the LCD screen, and measuring the relative light intensity and position information with a line array CCD, which is in good conformity with the theoretical results. The experimental device is inexpensive, simple in theory and intuitive in phenomena, and can be used as an optical demonstration device for theoretical and experimental classes.