Augmented reality (AR) display systems are developing towards ultra-miniaturization with the use of micro-light emitting diodes (Micro-LED) as miniature image sources in AR display technology. However, the Micro-LED with a large luminous angle, the collimating lens with a small size and high image quality, and the low optical efficiency at the edge of the field of view (FOV) and nonuniform illumination by vignetting of the collimating lens pose challenges for the design of AR optical systems. To solve these problems, a collimating lens was designed with high uniformity of illumination and high optical efficiency of the edge field of view for the diffraction grating waveguide by adding the calculated aspherical field lens. Then, by analyzing the theory in detail, its surface shape parameters were solved, and the lens with relatively uniform illumination was designed. The new collimating lens had a diagonal FOV of 41.2°, an F/# (F^#) of 1.87, and a modulation transfer function greater than 0.5 at 125 lp/mm. The simulation results show that the illumination uniformity is relatively improved by 14%, and the optical efficiency of the edge FOV is relatively increased by 15%. The lens has good imaging performance, and can be applied in the ultra-small AR diffraction grating waveguide head-mounted display system.