Shear failure is a common phenomenon in deep engineering works, affecting both intact and structural rock masses. In particular, under high true triaxial unequal stresses (σ1 > σ2 > σ3), rocks exhibit significant disparities in the deformation, shear strength, and failure characteristic. However, the shear strength and deformation failure characteristics of rocks under true triaxial unequal stress remain unclear. In this work, the shear test apparatus was used to undertake true triaxial shear tests under different stress conditions. The shear deformation failure and strength of intact sandstone were investigated. The test results show that dilation in the normal direction and compression deformation in the shear direction. The normal stress plays a significant role in the shear deformation of intact sandstone. It is important to note that normal stress exhibits a positive correlation with shear strength and shear stiffness, whereas the effect of lateral stress on these parameters displays variability. Specifically, lateral stress exerts an influence on rock strength by modulating its internal structure. Furthermore, lateral stress may elevate the propensity for ductile fracture within the shear rupture zone, thereby mitigating brittle fracture in the rock.