This work investigates the effects of deformation mechanisms on the mechanical properties and anisotropy of rolled AZ31B magnesium alloy under uniaxial tension, combining experimental characterization with Visco-Plastic Self Consistent (VPSC) modeling. The research focuses particularly on anisotropic mechanical responses along transverse direction (TD) and rolling direction (RD). Experimental measurements and computational simulations consistently demonstrate that prismatic <a> slip activation significantly reduces the strain hardening rate during the initial stage of tensile deformation. By suppressing the activation of specific deformation mechanisms along RD and TD, the tensile mechanical behavior of the magnesium alloy was further investigated. The results show that basal <a> slip has the greatest impact during the initial deformation stage and basal <a> slip activation substantially affects the deformation behavior of AZ31B alloy, causing marked decreases in both yield and tensile strength along RD. Under tensile loading along TD, prismatic <a> slip not only exhibits a synergistic effect on yield strength, but also dominants work hardening during the initial plastic deformation.