The effects of the water/TEOS ratio, pH, temperature and alcohol/TEOS ratio on the degree of polymerization and gelation time in the acid-catalyzed sol-gel polymerization of TEOS have been studied systematically with Monte Carlo simulation. Although linear polymerization by bimolecular reaction was assumed, the reversibility of hydrolysis and condensation, the substitution effect and the effect of molecular separation were considered. The enhanced gelation with water/TEOS ratio resulted from increased water-producing condensation between fully hydrolyzed chain polymers, When pH varies, the fastest gelation occurs when the ratio of condensation to hydrolysis rate moves toward 1 as successive condensation after hydrolysis becomes possible. The accelerating effect of temperature enhances diffusion and increases the rate ratio of condensation to hydrolysis. Alcohol retards gelation due to its dilution effect, The qualitative results obtained in this model explain the experimental behaviors of sol-gel polymerization of TEOS, especially the change in the degree of polymerization, and gelation time with the experimental variables.