By using industrial sodium silicate solution as raw material，high purity SiO2 powder was successfully synthesized by the split-step carbonation method.The relations between pH value of end point and the removal percentage of impurity at the first carbonation and the purity and yield of product SiO2 powder at the second carbonation were studied.The SiO2 powder was characterized by using XRD，SEM，IR and composition analysis.The results showed that when the pH value of end point at the first carbonation was 10.9，the purity of SiO2 prepared was up to 99.9%.The SiO2 powder synthesized was amorphous with regular sphere shape，uniform size and no reunion.The reaction mechanism was also discussed.