Abstract: In this work,spectrophotometry was used to characterize the grey point of the hydrolysis process of titanium dioxide by sulfuric acid process. Based on the relationship between the transmittance and time during two hydrolysis processes （without and within addingexternal seeds）,the impact of hydrolysis process on the grey point was investigated.Further,according to the current hydrolysis process within adding external seeds,the research of the effects of hydrolysis degree at grey point on H₂TiO₃ particle size,and the relationship between hydrolysis degree and the transmittance are carried out,aiming at determine the transmittance range corresponding the better H₂TiO₃ particle size with the established scanning wavelength and dilution ratio.