Abstract: Due to the growing demand for lightweight transportation equipment, magnesium alloys are increasingly employed in engineering structures. This study focuses on AZ31B magnesium alloy thin-walled tubes, conducting a series of experiments under various stress states to accurately capture the hardening and failure data of the material. The experimental results reveal pronounced tension-compression asymmetry in both the hardening behavior and fracture strain of AZ31B alloy. Constitutive and fracture models tailored to AZ31B were proposed to describe its hardening and fracture characteristics. These models were subsequently implemented into LS-DYNA via a user-defined material subroutine (UMAT), and validated against experimental data to ensure their accuracy. Three-point bending tests on thin-walled tubes were conducted alongside numerical simulations. Comparisons between simulations and experiments demonstrate that the developed constitutive and fracture models effectively characterize the deformation and fracture behavior of AZ31B magnesium alloy under complex stress conditions, confirming their applicability in predicting the mechanical response of magnesium alloy components under intricate loading scenarios.