Characteristics of $TiO_2$nanoparticles controlled by precursor flow rate and reaction temperature in chemical vapor condensation process were interpreted in the view of decisive reaction factors, i.e. supersaturation ratio, concentration of vapor molecule, collision frequency and rate, and residence time, which directly affect the particle size and size distribution in CVC reactor. As results, the increases of precursor flow rate and reaction temperature induced the increase in the average sizes of $TiO_2$ nanoparticles in CVC reactor by acceleration of coagulation growth due to the increase of collision between $TiO_2$vapor molecules and particles. The effects of reaction factors on the characteristics of$TiO_2$nanoparticles were discussed with considering particle formation process in CVC reactor under given process parameters.??????????????適잖????適잖???