The silica sol is a kind of colloid solution, silica drop dispersing in water or solvents.Silica sol was prepared by sol-gel method from tetraethoxy silane (TEOS)with the ethanol as solvent and dilute hydrochloric as catalyst .Orthogonal test was used to study the effects on silica sol stability such as the mole ratio of water and TEOS , the mole ratio of EtOH and TEOS, pH , the mole ratio of DMF and TEOS and the temperature .The effects of the above factors can be used to control the silica sol stability .The results show that the mole ratio of EtOH and TEOS exhibits significant effect on the silica sol stability , the silica sol stability increases with the increasing mole ratio of EtOH and TEOS .The next is the mole ratio of DMF and TEOS .DFM makes gelation time become long .The other effects are least .The effect of temperature is the least, sol stability decreases with the increasing temperature .