W-Y binary alloy has potential applications in the first wall material for nuclear fusion device. Mechanical properties have important effects on material processing and application. However, the mechanical properties of W-Y alloy are rarely reported in the literature. In this paper, the effect of yttrium contents on the fundamental mechanical properties of W-Y alloys has been studied by using first-principles method based on the density functional theory. The mechanical constants of W_1-xY_x (x=0.0625,0.125,0.25,0.5) alloys were calculated for different compositions in solid solution model. According to the calculated mechanical constants, the mechanical properties are analyzed. Our results show that the elastic constants, bulk modulus, Young’s modulus and shear modulus of W-Y alloys decrease non-monotonically with the increase of Y concentration, indicating that the doped Y decreases the mechanical strength of W materials. Based on the mechanical characteristic, such as B/G, Poisson’s ratio ν and Cauchy pressure C", the ductility and toughness of the W-Y alloys are significantly improved with the increase of Y concentration. When the Y contents reaches 0.25, the resistant and ductility of W-Y alloy are largely enhanced. Through the analysis of the density of states, W-Y alloy metallic properties begin decreases and then increases as the concentration of Y increases.