Inertial confinement fusion (ICF) establishment needs lots of high quality, large caliber and non-linear optical material potassium dihydrogen phosphate (KDP), which is water-soluble crystal. It is necessary to prepare a moisture-barrier protective film with good performance on the surface of KDP crystals. Antireflective SiO2 coating has been prepared by tetraethyl orthosilicate (TEOS) and sol-gel route with dip coating method. The surface of SiO2 film was disposed with teflon AF2400. The properties of the AF2400-SiO2 composite film had been characterized and measured by atomic force microscope (AFM), Fourier transform infrared (FTIR), UV-VIS-NIR spectroscopes etc. The experimental results show that the light transmission of AF2400-SiO2 composite film is 97.7% at 355 nm, the refractive index is 1.21. The AF2400-SiO2 composite films have fine water-repellent performance, high laser damage threshold (19.5 J/cm2) and excellent optical property. The composite film can be used for protection of KDP crystal.