(CH3)2Si(OC2H5)2 as precursor, a sol of good stability is prepared by sol-gel method and organic synthesization. After the sol is coated it on phosphate laser glass by rotating way, moistureproof film is worked out, having a transmittance of 96.5% after heated. The film has a good morphology, roughness of mean square (RMS) of 1.659 nm and roughness of average (RA) of 1.321 nm. The damaged threshold of the moistureproof film is high to 10～14 J/cm2, tested by a laser of wavelength of 1053 nm and pulse width of 1 ns. In the period of 5 years on “Shenguang Ⅱ” high power laser equipment, it behaves good moistureproof performance , and tryouts on “Shenguang Ⅲ” model.