By using a new theoretical glass transition temperature (T (g))-composition equation, T (g)'s of statistic binary copolymers obtained from MMA, St and AN were investigated in this article. The copolymers were prepared by bulk copolymerization using azo-bis-isobutyronitrile (AIBN) as initiator. The compositions and T (g)'s were determined by NMR and DSC, respectively. The monomer reactivity ratios were obtained by nonlinear fitting with Mayo-Lewis equation. Excellent fitting results were obtained when relations of T (g)'s of MMA-St, MMA-AN, and St-AN copolymers with their compositions were investigated by using a new equation which assumed additivity of bond stiff energy (Liu et al. J Phys Chem B 112:93-99, 2008). This equation contains mole fractions of triads and T (g)'s of corresponding periodic copolymers. Compared with the widely used Johnston equation and Barton equation, the new equation showed its superiority. Meanwhile, T (g)'s of the assumed periodic copolymers that have not been acquired were tentatively predicted which may provide useful information.