Stress relaxation is a critical stage for some accurate forming processes, such as hot sizing. In the relaxation stage, the part keeps the deformed status, meanwhile the internal stress decreases as time increases. Material characterization and constitutive modeling for the stress relaxation behavior are the fundamental issues for these forming processes. The present work focus on the material characterization and validation of relaxation behavior of Ti-4Al-1.5Mn alloy at high temperature. Firstly, constitutive models for the relaxation behavior at 500℃, 600℃ and 700℃ are established based on the stress relaxation tests. Further, the models are applied to finite element software ABAQUS to simulate the influence of stress relaxation on the springback after V-bending. The results show that the stress relaxation is controlled by temperature and relaxation time. The relaxation process can be divided into two stages. In the first stage, the stress decreases fast. In the second stage, the stress decreases slowly. Finally the residual stress decreases to a limit value, which is defined as relaxation limit. Both hyperbolic sine and time hardening model can predict the variation of stress relaxation. The predicted springback shows promising agreement with the corresponding experimental observations. Hyperbolic sine model is more reliable than the time hardening model. The study is of guiding significance for the design of precise forming process by means of relaxation process.