<p>This paper aims to investigate the effects of confining pressure and stress paths on the mechanical behaviors and failure characteristics of medium-grained sandstone. For this purpose, a series of triaxial monotonic and multi-stage cyclic loadings were conducted on red sandstone from Rizhao, Shandong Province. First, the conventional triaxial compression tests were performed on the red sandstone to analyze the influence of confining pressure on the strength and deformation parameters of the specimens. Subsequently, the stress–strain curves, axial strain evolution and elastic modulus variation of the red sandstone specimens under different confining pressures were analysed by the results of multi-stage fatigue tests. Finally, the post-failure red sandstone specimens were scanned using X-ray micro-computerized tomography (CT) scanning, and the failure behaviors of the red sandstone specimens were explored in detail through CT scanning section analysis and 3D reconstruction, revealing the impacts of lateral constraints and stress modes on the fracture mechanism of the red sandstone specimens. The results showed that the peak strength of the sandstone specimens increased non-linearly with the increase of the confining pressure, and the relationship could be well-described by the Hawke–Brown criterion. Under uniaxial conditions, multi-stage cyclic loading resulted in a 2.89% increase in the strength of the specimens compared to monotonic loading, while single-stage cyclic loading resulted in a 14.2% decrease in the strength of the specimens. Under triaxial multistage cyclic loading, the mechanical parameters of sandstone specimens showed obvious stage characteristics. With the increase of confining pressure, the sandstone transitioned from splitting failure to shear failure, and the macroscopic fracture angle gradually decreased. Compared with the confining pressure factor, the influence of the cyclic loading path on the fracture characteristics of sandstone was relatively limited. The crack rates of failed sandstone specimens generally followed the sequence of uniaxial multistage cyclic loading &gt; uniaxial single-stage cyclic loading &gt; conventional uniaxial compression &gt; conventional triaxial compression &gt; triaxial multistage cyclic loading. As the height of the specimen increases, its internal crack rates first rise and then decrease. The findings could improve the understanding of the mechanical behaviors and fracture mechanisms of rocks under monotonic and cyclic loading.</p>