Abstract: The laser scattering technology was used to monitor the aggregation process of silica particles under various conditions and the Smoluchowski equation was used to describe the process theoretically, in which the coagulation kernel was determined by using molecular reaction kinetic method in terms of fractal. The parameters of equation were obtained from the comparison between numerical solution and experimental values and the effects of pH value and temperature were analyzed. The fractal dimension thus determined agreed with computer simulation.