As a pre-treatment unit for preparing solar-grade silicon, hydrometallurgical route could remove most metallic impurities in silicon dioxide (SiO2) and raise the final product yield. Acid leaching of SiO2 could reduce the cost and energy consumption of industrialized development. Combined with high purity of reducing agent, the successor process of pyrometallurgy can also achieve “continuous casting”. Factors such as the mass fraction of leaching agent, time, the particle size of SiO2, and the liquid-solid ratio were investigated, and the samples were characterized by ICP-OES, SEM, etc. The optimal reaction conditions were as follows: w(HF) = 2%, w(H2C2O4) = 3%, w(HNO3) = 30%, reaction time 4h, the average size of SiO2 powder particle 100 mesh ~ 120 mesh, the liquid-solid ratio 4:1, and room temperature 30℃. It was found that the final removal rates of Fe, Al, Ca, P impurities could reach 99.99%, 14.02%, 73.27%, 60.00% respectively and the mass fraction of total amount of impurities could be reduced to 1.465×10-4.