Abstract <p>The hot deformation behavior of AA2099 Al-Li alloy was analyzed constitutively to model flow stress during thermo-mechanical processing. In order to obtain the true stress-strain curve data of AA2099 Al-Li alloy, isothermal uniaxial compression tests were carried out using a Gleeble 3800D thermo-mechanical simulator in the strain rate range of 0.01–10 s^–1 and deformation temperature range of 360 – 520°C. Based on the experimental data obtained here, three types of constitutive material models were developed: modified Johnson-Cook model, strain compensated Arrhenius model and microstructure-based model. For these three models, a modification was made to increase the prediction accuracy of high temperature flow stress. The prediction accuracy was estimated by means of the average absolute relative error and correlation coefficient, with 5.09% and 0.9928 for the modified Johnson-Cook model, 6.12% and 0.9820 for the strain compensated Arrhenius model, and, 1.58% and 0.9994 for the microstructure-based model. The flow stress predicted by the proposed microstructure-based model was in good consistent with the experimental results. This indicates that the proposed microstructure-based model can describe the hot deformation behavior of AA2099 Al-Li alloy very accurately. The developed constitutive material models are of great significance in the simulation and optimization of hot working processes of AA2099 Al-Li alloy.</p>