The transmission of porous silica antireflective (AR) coating after heat treatment is correlative with environmental relative humidity because there are many Si-OH hydrophilic groups on the coating surface. The aim of the experiment is to add hydrophobic groups to the coating to enhance its hydrophobic performance and improve its stability. In this paper, Si-CH3 non-polar hydrophobic groups appear on the coating surface through dash with organic silica, raising its hydrophobic performance, and thus the stability and life of AR coating are improved greatly. When the molar content of organic silica (Si-CH3) is 17.5% (mass concentration 0.35%), the antireflectivity of coatings is high, while the performance of high laser damage threshold is not affected.