To analyze the influence of confining pressure and pore air pressure on the rock mechanical properties under different stress paths, conventional triaxial tests under the gas undrained condition were carried out on a low-permeability and tight red sandstone. The experimental results show that the confining pressure has a strengthening effect on the sandstone. As the confining pressure increases, the strength and ductility of the rock increase significantly, and the rocks eventually show the form of shear failure. The pore air pressure reduces the compressive strength, while increasing the brittleness and internal tension of the sandstone, by damaging the internal continuous structure and leading to the occurrence of splitting failure plane.