Magnesium (Mg) single crystal specimens with three different orientations were prepared and tested from room temperature to 733 K in order to systematically evaluate effects of temperature on the critical resolved shear stress (CRSS) of slips and twinning in Mg single crystals. The duplex non-basal <a> slip took place in the temperature range from 613 to 733 K when the single crystal samples were stretched along the <0110> direction. In contrast, the single basal <a> slip and prismatic <a> slip were mainly activated in the temperature range from RT to 733 K when the tensile directions were inclined at an angle of 45° with the basal and the prismatic plane, respectively. Viscoplastic self-consistent (VPSC) crystal modeling simulations with genetic algorithm code (GA-code) were carried out to obtain the best fitted CRSSs of major deformation modes, such as basal <a> slip, prismatic <a> slip, pyramidal Ⅱ <c+a>, {1012} tensile twinning and {1011} compressive twinning when duplex slips accommodated deformation. Additionally, CRSSs of the basal <a> and the prismatic <a> slip were derived using the Schmid factor (SF) criterion when the single slip mainly accommodated deformation. From the CRSSs of major deformation modes obtained by the VPSC simulations and the SF calculations, the CRSSs for basal <a> slip and {1012} tensile twinning were found to show a weak temperature dependence, whereas those for prismatic <a>, <c+a> slip and {1011} compressive twinning exhibited a strong temperature dependence. From the comparison of previous results, VPSC-GA modeling was proved to be an effective method to obtain the CRSSs of various deformation modes of Mg and its alloys.