Response surface methodology was adopted to optimize waterglass preparation process, and silica aerogels were synthesized under ambient pressure drying with optimum condition. Experimental results show the optimum conditions are: alkali silica ratio 3∶10, alkalinity 10%, and reaction temperature 90 ℃. The morphology structure and other properties of silica aerogel based on diatomite were characterized by N2 physical adsorption, XRD, FESEM, TEM, FTIR and TG/SDTA measurement. The results indicate that silica aerogel is crack free amorphous state solid, with the density 0.132～0.143 g/m3 and the specific surface area 755.5 m2/g, and it exhibits a sponge structure and a narrow pore size distribution. In addition, the hydrophobicity of aerogel can maintain up to 400 ℃。