To study the influences of rock mechanical parameters on the penetrating rate of a tunnel boring machine (TBM), a 3D discrete element model, namely, 3D distinct element code (3DEC), was used to build simulated models on rock fragments using a TBM cutter based on the geological conditions of the west route of the South-to-North Water Transfer Project. The change rule of the TBM penetrating rate caused by different rock mechanical parameters was analyzed. The line graph of the relationship between the TBM penetrating rate and rock mechanical parameters was fitted using the least squares method. Results show that the TBM penetrating rate will decrease with an increase in uniaxial compressive strength and elastic modulus. By contrast, it will increase with an increase in rock Poisson’s ratio. This finding is in accordance with the result of the finished project. A numerical foundation was provided for the TBM tunneling of diversion tunnels in the west route of the South-to-North Water Transfer Project.