<p>The failure modes of roadway surrounding rock are significantly influenced by the coupled effects of stress magnitude and path. This study first established the transformation relationships among the principal stress coordinate system, geographic coordinate system and roadway coordinate system, determining the direction cosine matrices of the basis vectors for each coordinate system. Next, the matrices were used to derive the stress analytical function for any unit around the roadway. Then, a numerical calculation method for the plastic zone of roadways applicable to arbitrary stress paths was proposed and the weight effects of different directional stress components on the morphological characteristics, expansion range and maximum failure orientation of the plastic zone were analysed. The results indicated that stress amplitude primarily regulated the degree of stress concentration in the surrounding rock and the expansion scale of the plastic zone, while stress direction was the key factor leading to the asymmetric and heterogeneous distribution of the plastic zone. Specifically, the normal stress component was the dominant factor controlling the expansion range and morphology of the surrounding rock plastic zone. When the shear stress component was coupled with the roadway axial direction, it only exerted a secondary influence on the expansion range and morphology of the plastic zone. However, when the shear stress component was independent of the roadway axial direction, it induced a significant spatial rotation effect on the stress field and the morphology of the plastic zone in the surrounding rock.</p>