Aiming at the problem that the mask deformation due to its own gravity during the traditional contact exposure process, which can introduce nonnegligible linewidth errors and position errors, a set of high-precision fabrication methods for large-diameter quartz substrate diffractive lenses was proposed. A high-flatness and high-strength metal calibration fixture with vacuum channel on the back is adopted to attract the mask, and the pressure difference between the upper and lower surface of the mask is used to make it highly fit with the fixture to ensure the high flatness of the mask. Then the fixture is removed after all areas of the quartz substrate are in close contact with the structure surface of the mask. After the contact exposure and development are completed, the large-diameter quartz substrate is etched by reactive ion etching technology, and finally a high-precision micro-nano structure is obtained. The results of finite element analysis show that the deformation of the mask was reduced from 28.85 μm to 0.88 μm after using the calibration fixture. The experimental results show that the wave-front error of the 430mm two-step quartz substrate Fresnel diffraction lens prepared by this method is better than 1/25λ, the average diffraction efficiency is 38.24%, reaching 94.35% of the theoretical value, and it has well focusing and optical imaging effect.