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, α_p 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 α_p phase decreased, the continuity of β_trans phase increased and α_s phase coarsening in air-cooling process, The volume fraction of α_p 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-α_s phase in the bimodal microstructure improves the strength of the alloy and the α_p 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.