In 2Y-TZP powders calcined at temperature range of 80$0^{circ}C$0 to 150$0^{circ}C$, the effect of stabilization and the transformability of tetragonal phase on the tetragonal to monoclinic transformation have been investigated. The transformability of tetragonal phase in calcined powders shows maximum at the calcination temperature of 130$0^{circ}C$. This result is explained by a combined effect of the increase of particle size and of constrained force among the particles with increasing the calcination temperature. The amount of transformed monoclinic phase with calcination temperature after quenching in liquid nitrogen, stress induction and isothermal aging at 25$0^{circ}C$is also explained by the transformability of tetragonal phase determined by the sum of particle size effect and constraint effect.