Using a base catalysis for the hydrolysis of tetraethyl orthosilicate (TEOS), porous silica antireflective film are prepared by in-situ sol-gel process and normal atmosphere drying with the introduction of N, N-dimethylformamide (DMF). Thermal stability in drying process of the SiO2 sol is studied by Netzsch thermal analyzer; the structure and morphology of these samples are characterized by scanning electron microscope (SEM); the effect on optical properties of porous silicon thin films are measured by spectrophotometer. The results show that DMF effectively prevents the gel from cracking and inhibits the formation of particle clusters, which makes silica particles form a network and prepare silica films easily. DMF can also improve the transmittance of film higher than 99% in 300~1000 nm region.