SiO2 sol is prepared using the sol-gel process with tetraethyl orthosilicate as the precursor, and the porous SiO2 antireflective coating is fabricated using the dip coating method. Further, the surface of the SiO2 coating is covered using a methyltriethoxysilane (MTES) prepolymer. The objective of the experiment is to use the hydrophobic MTES prepolymer film as a cover of the surface of the SiO2 coating and to modify the surface of the coating. Ultimately, we intend to improve the environmental stability of the porous SiO2 coating. Thus, an surface-modified composite coating exhibiting a peak transmission of 99.67%, refractive index of 1.231, and water contact angle of 123.6° is obtained. Furthermore, the peak transmission of the coating becomes as high as 99.09% and its stability considerably improves after being maintained at a relative humidity of approximately 95% for 475 days. It can also be observed that the modified coating surface is smooth and that the laser-induced damaged threshold is 24.5 J/cm 2.