In inertial confined fusion systems, SiO₂ sol-gel antireflective films have been widely used for relief-free planar transmission optical elements. However, owing to the lack of a reliable relief surface coating process, this antireflection method cannot be applied to beam sampling grating (BSG). In this study, meniscus coating and spin coating methods were studied for coating a SiO₂ sol-gel antireflective film on the relief surface of BSG. Optical microscopy, optical profilometry, and atomic force microscopy were used to detect the surface morphology of the coated grating. The size and uniformity of the zero-order and negative first-order diffraction efficiency of the grating were tested. Results show that compared with the spin coating method, the grating surface coated using the meniscus coating method is smoother, the consistency of groove filling is better, the retention of the original groove is higher, the repeatability of the process is better, and the film thickness is more uniform. Diffraction efficiency test results show that coating the SiO₂ sol-gel antireflective film using the meniscus coating method can effectively improve the zero-order diffraction efficiency of BSG, which increases by 3.8%. Furthermore, the meniscus coating method facilitates a better uniformity of the zero-order and negative first-order diffraction efficiency than the spin coating method.