In order to avoid the damage effects of ice formation during freezing, the vitrification technique for cryopreservation of the biological materials has arrested much public attention recently. In this paper, a semi-empirical model developed by Boutron has been modified. The exact analytical expressions obtained here can be used to construct those temperature-time-transformation(TTT)curves for isothermal crystalli- zation and continuous-cooling-transformation (CCT)curves for nonisothermal crystallization, from which the critical cooling rates required for vitrification of cryoprotective solutions can then be predicted directly. It is found that the glass-forming tendency of 1, 2-propanediol is higher than ethylere glycol and glycerol, the critical cooling rates can be reduced by adding 1,2-butanediol into 1,2-propanediol solution.