In this paper, a multilayer holographic flat waveguide display system has been proposed to realize the full-color display function of the augmented reality head-mounted display system. Furthermore, the diffraction principle, grating constant, and corresponding diffraction wavelength are investigated. First, the grating equation and total reflection theory were used to introduce the limiting relationship between the coupling grating constant and the transmitted light wavelength of the holographic planar waveguide. Second, to realize pupil expansion, the restrictive relationship between turning, out-coupling, and in-coupling gratings were applied. Third, the single-layer holographic flat waveguide display structure for 550-nm green light was simulated and designed. Next, based on the single-layer holographic planar waveguide, a three-layer holographic planar waveguide display system with 685 nm, 550 nm, and 437 nm as the three primary colors was established. Finally, the light output effect of three-layer holographic planar waveguide processing samples was examined using digital light processing projection system as a light source. The experimental results show that the three-layer holographic planar waveguide realized pupil expansion and panchromatic display. Moreover, multilayer holographic planar waveguide realized a full-color display of an augmented reality head-mounted display system.