In weak strata， the mechanical effect of tunnel anchoring and shotcrete support primarily results in the formation of a bearing ring based on the surrounding rock near the spatial boundary. Based on the corresponding relationship between the relevant factors in rock mass rating （RMR） system and the factors involved in geological strength index （GSI） of rock mass， concise ways to quantify sub-items of GSI and determine its total value were obtained. Based on the equivalent conversion relationship between the internal friction angle， cohesion force and Hoek-Brown （H-B） constants of rock mass as well as the sliding failure mode of Rabcewicz’s shear wedge， calculation approaches of the bearing ring resistance and its safety factor equivalent to H-B yield criterion were established. The case study results indicate that the safety factor of the bearing ring analyzed based on the H-B criterion is consistent with its actual state， while the safety factor based on the Mohr Coulomb （M-C） criterion is too conservative. The mechanical mechanism and overall characteristics of the bearing ring are determined by the mechanical properties of its rock mass itself and the support structure constituted by rock bolts and shotcrete and steel ribs. The thickness of the bearing ring is determined by the length of rock bolts. The resistance of the bearing ring is first positively correlated with the length of rock bolts， and after exceeding a certain value， it becomes negatively correlated. The main effectiveness of steel ribs is to avoid excessive deformation and loosening of surrounding rocks in the early stages. Shotcrete is the main source of bearing ring tightening force （confining pressure）. The mechanical properties of rock mass are the dominant factor for the magnitude of bearing ring resistance.