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_{: In order to study the flow stress characteristics of Ti2AlNb alloy under high strain rate conditions, the quasi-static tensile curves was obtained with electronic universal testing machine, and the dynamic true stress-strain curves under high strain rate was obtained with split Hopkinson pressure bar. The results show that the flow stress of Ti2AlNb alloy has a strong sensitivity to strain rate conditions. Ti2AlNb alloy has strain work-hardening, strain rate strengthening and plasticity-increasing effect under high strain rate conditions. The adiabatic temperature rise in the plastic deformation process has a softening effect on the material. It is found that the appearance of adiabatic shear band is the main reason for the rapid decrease of flow stress under the condition of high strain rate loading. The dynamic constitutive relation of Ti2AlNb alloy at room temperature was obtained by fitting the experimental data with improved Johnson-Cook constitutive model. Compared with the experimental results, it is proved that the improved model can predict the flow stress of Ti2AlNb alloy well under high strain rate conditions.}