Abstract:The hot-rolled Zr-2.5 Nb alloy plate are heated in the high temperature region (750 ~ 850℃) of α + β two-phase region for different holding time (1 ~ 10 h), and then cooled to room temperature in different ways, the effects of different heat treatment conditions on the microstructure type, microstructure characteristic(phase content、grain size , etc.) and mechanical properties of the alloy are studied.The results show that there are two different diffusion transformation in the air-cooling and furnace-cooling process compared with water-cooling. In the air-cooling process, nano-scale lath αs phase is precipitated inside the β phase to form the bimodal microstructure. During the furnace cooling process, αp phase directly consumes β phase and grows up to form equiaxed microstructure.With the increase of heat treatment temperature and the holding time, the volume fraction of αp phase decreased, the continuity of βtrans phase increased and αs phase coarsening in air-cooling process, The volume fraction of αp phase in the equiaxed microstructure in furnace-cooling process remains basically unchanged, the average grain size increases, and the continuity of the residual β phase is enhanced. Compared with the equiaxed microstructure, the nano-αs phase in the bimodal microstructure improves the strength of the alloy and the αp phase ensures that the alloy has good plasticity. Reducing the heat treatment temperature and holding time can make the bimodal structure alloy have excellent combination of strength and plasticity.