Abstract: The theory of butterfly-shaped plastic zones holds significant importance for controlling the deformation and failure of roadway surrounding rocks. The butterfly leaf angle, as a critical parameter representing the extension direction of the butterfly leaves, reflects the dynamic characteristics of the extension direction. However, due to the implicit nature of the boundary equation for the butterfly-shaped plastic zone, the butterfly leaf angle cannot be directly solved. Therefore, this study reformulated the boundary equation mathematically and, based on this, analyzed and summarized the evolution law of the butterfly leaf angle. The study integrates theoretical derivations and numerical simulations to analyze the key influencing factors in the evolution of the butterfly leaf angle, including the cohesion C, internal friction angle φ, lateral pressure coefficient λ, minimum principal stress P₃, and tunnel radius a of the surrounding rock. By combining theoretical formulas and numerical simulations, the mechanisms through which these factors affect the butterfly leaf angle were examined, and the consistency between theoretical and simulated results was validated. The findings revealed the following: ① With the increase in the internal axis characteristic radius, the butterfly leaf angle first decreases and then increases. During this change, the characteristic radius R_1t corresponding to the minimum butterfly leaf angle and the upper boundary of the increase interval can be determined through calculations. ② The influencing factors of butterfly leaf angle evolution include cohesion C, internal friction angle φ, lateral pressure coefficient λ, minimum principal stress P₃, and tunnel radius a. Under different influencing factors, the magnitude of the butterfly leaf angle exhibits varying correlations with each factor. ③ The theoretical calculations and numerical simulation results exhibit high consistency in the evolution law of the butterfly leaf angle. The evolution trajectory is characterized by a “concave-up” or “concave-down” shape. Different influencing factors result in varied paths of the trajectory, with discrepancies in the extreme values and convergence behavior under different paths. These results provide a theoretical basis for understanding the expansion behavior of plastic zones under complex roadway conditions, offering technical support for optimizing roadway support design and assessing the stability of surrounding rocks. Future studies could further extend to analyzing the evolution of the butterfly leaf angle under nonlinear material models and dynamic loading conditions.