Abstract: Tunnel overbreak will have an adverse impact on the surrounding rock and support structure of the tunnel. It is of practical significance to select the appropriate support parameters to fill the gap and reduce the impact of overbreak. Based on the Yunwushan Tunnel project of the Bitong Line of Chongqing Suburban Railway, this paper uses analytical and numerical simulation methods to study the stress distribution of surrounding rock without support in the overbreak tunnel, and analyzes the stress and displacement distribution of surrounding rock and supporting structure under three different filling parameter schemes at the overbreak gap, namely, covering all with concrete, spraying equal thickness concrete gap grouting, expanding steel arch, and increasing section. Compared with that of an ideal non-overcut tunnel excavated according to the designed contour line, the study obtains the following conclusions: the radius of the plastic zone has a linear relationship with the excavation radius, and the unevenness of the excavation radius will lead to the unevenness of the plastic zone. Overbreak will increase the stress of the supporting structure, and the supporting structure is sensitive to the bias load caused by uneven overbreak. The simulation results of the overbreak tunnel with different support parameters show that different support parameters have their own advantages in different aspects, so reasonable filling parameters should be selected according to the actual situation.