Abstract: Based on a complex karst tunnel of an expressway, numerical simulation and field test methods are used to analyze V level surrounding rock deformation, supporting structure and plastic zone stress characteristics under the action of the stress field, seepage field and stress field coupling field in this paper. It also discusses the distribution law of seepage pressure and support deformation of tunnels with different grouting rings. The numerical results show that the displacement of surrounding rock and initial support under the coupling of seepage field and stress field is greater than that under the condition of considering only stress field. In order to ensure the safety of tunnel supporting structure, we simulated the grouting effect under different grouting ring thickness, and obtained that the grouting ring thickness under the effect of stress field is at least 8m, whereas the thickness of grouting ring should be at least 10m when the two fields are coupled. Finally, through the deformation monitoring data, it is verified that the calculation of grouting circle thickness is reasonable, which provides a reference for similar complex karst tunnel engineering in southwest area.