In this paper, the mechanical properties of Cu 3 Si were researched by the first-principles method. And the method based on density functional theory (DFT). The exchange correlation energy function adopts the generalized gradient approximation (GGA). Approximately calculate the bulk modulus, Young's modulus, shear modulus and Poisson's ratio of Cu 3 Si crystal by Voigt-Reuss. The B/G value of Cu 3 Si is 3.66, and it can be considered that Cu 3 Si is a ductile material. The anisotropy index A U is 6.169, indicating that the anisotropy of Cu 3 Si is extremely obvious. The anisotropy indexes A B and A G are 0.004 and 0.381, respectively, revealing the weak anisotropy for bulk modulus and obvious anisotropy for shear modulus. The shear anisotropy indexes A 1 , A 2 and A 3 are 0.605, 0.605, 1.005, respectively, showing that the Cu 3 Si crystal exhibits obvious shear anisotropic characteristics at {100} and {010} planes, and there is almost no anisotropy at {001} plane. Moreover, The orientation of the bulk modulus, Young's modulus and shear modulus, as well as their maximum and minimum values were identified.