Taking the core samples from the deep strata of the northern mountains of Gansu Province as the research object, this study explores the short-term and long-term mechanical properties of the North Mountain granites under different confining pressure conditions, thereby providing theoretical support for the deep construction of the underground laboratory for nuclear waste geological disposal in the North Mountain. Conventional triaxial compression tests and creep tests were carried out to investigate the mechanical characteristics of the North Mountain granites under different confining pressure conditions. The main conclusions are as follows: (1) In the triaxial compression tests, the North Mountain granites experienced five stages: initial crack closure, linear elasticity, stable crack propagation, unstable crack propagation, and post-peak softening. With the increase of confining pressure, the typical characteristic stress and peak strain increased significantly, showing a clear confining pressure effect, and could be well described by linear fitting. (2) The multi-stage creep tests revealed that under different failure stress levels, the North Mountain granites experienced the attenuation stage, the steady-state stage, and the acceleration stage, with the attenuation stage and the steady-state stage alternating; and (3) In terms of macroscopic failure characteristics, under low confining pressures, the North Mountain granites exhibited mixed failure of tension and shear; under higher confining pressures, macroscopic main cracks penetrating the surface of the specimens appeared, presenting a typical shear failure mode.