Abstract: Atomic structure evolution and diffusivity during the cooling of Zr₅₀Cu₅₀ metallic liquid are studied by molecular dynamics (MD) simulation. Based on the theory that free volume is equal to the volume difference between the amorphous materials and their crystalline counterpart, a new method of annihilating rate of free volume has been developed and applied to predict the critical microscopic glass transition temperature. The predicted critical temperature T_c was 969.5K, which is close to the MCT(mode-coupling theory) value of 978.4K, and the caloric glass transition temperature T_g was 731K, which is also close to the value of 725K determined from the curve of average atomic volume with temperature. Without calculation of diffusion coefficients at a serial of specified temperatures, the developed method is more convenient than former methods to calculate T_c and T_g.