Abstract: Roadway excavation induces redistribution of the principal stress field in surrounding rock accompanied by rotation of the principal stress directions, which readily leads to engineering problems such as surrounding rock instability and support failures, seriously threatening the safety of soft rock roadways. To investigate the rotation characteristics of principal stresses during excavation, this study adopts the Mohr's circle spatial coordinate transformation method and establishes a critical failure criterion for soft rocks considering principal stress orientations. The evolution of principal stress magnitude and orientation is analyzed, and the mechanism of excavation-induced surrounding rock instability is revealed. Results indicate that the principal stress field experiences three stages: initial stability, severe disturbance, and new equilibrium. Stress concentration is most obvious at the two sidewalls, reaching 152% of the initial stress, with the principal stress directions restored to their initial orientations at the new equilibrium stage after serve disturbance. Principal stresses at the roof and floor are 132% and 121% of the initial stress, respectively, with the maximum and minimum principal stress directions interchanged after disturbance. Based on the rotation trajectories of principal stresses in rock masses with weak planes under different excavation directions, optimal roadway advancement directions are proposed for single, multiple, and random weak planes. The findings provide a theoretical reference for stability control of soft rock roadways. The research findings can guide the optimal advancement direction for soft soil roadways containing weak planes, providing new ideas for the stability control of surrounding rock.