Transition of zirconium alloys during uniform corrosion is not expected but inevitable, since it accelerates the degradation of corrosion property. Up to now, proposed transition mechanisms have not clearly illustrated the critical behavior of interfacial t-ZrO2 and other oxide features under the critical transition condition. Therefore, study on the under-transition sample was carried out. Microscopically, the monoclinic stress increases after transition, strongly supporting the occurrence of transformation from t-ZrO2 to m-ZrO2. A sudden stress decrease in t-ZrO2 occurs in pre-transition region of the under-transition sample. This decrease might be attributed to formation of permeable paths which induce consumption of interfacial oxygen vacancies. This critical behavior possibly destabilizes the grown t-ZrO2 grains. And the post-transition regions will propagate after t-ZrO2 transformation. The transition region in the oxide consists of lateral cracks propagated transgranularly and large numbers of interconnected pores, both of which may originate from t-ZrO2 transformation. Current works suggest that three critical behaviors of t-ZrO2 induce oxide fracture and corrosion transition. The growth nature and evolution mechanism of t-ZrO2 are further illustrated. Even though t-ZrO2 layer similarly evolve as the ZrO suboxide layer, the unstable nature of t-ZrO2 indicates that it is severely affected by grain size, stress value and chemical composition.