A type of 4/λ-4/λ ultra-broadband antireflective coating made from modified low refractive silica and high refractive silica layers has been developed by sol-gel dipping method for amplifier blastshields of the SG Ⅱ.First layer (high refractive index silica) is deposited by 200℃ baking post-treatment step.Second layer (low refractive index,n=l.20) is deposited by acid catalyzed silica modified ultra-low refractive index silica sol.Thermal baking step temperature does no less than 500℃ during 60 minutes to offer chemical stability, ethanol scratch-resistance properties and water washing resistance.The average of residual reflection of both side coated fused silica glass is less than 1% in the spectra from 450nm to 900nm.Transmission gain has been evaluated taking into account the light angular ,the result have shown that transmission gain increase with light incidence,even at 60 degree the transmission spectra of broadband antireflective coating still effectively cover the main absorption peak of Nd∶glass.