As a common geomorphic form in karst areas, isolated peak plain area generally does not have the physical workload of investigation due to its steep terrain, so it is impossible to obtain parameters such as uniaxial compression strength of rock, rock mass integrity, groundwater and weak structural plane. The classification of tunnel surrounding rock is mainly based on the rock strength and rock integrity as the main discrimination indicators, and the groundwater, the occurrence of weak structural planes and the initial test stress state as the correction indicators. Due to the lack of corresponding judgment basis, the basic classification of tunnel surrounding rock cannot be carried out, which is mainly based on experience. Through the analysis of the existing survey data, based on the liner karst ratio exposed by the drilling of the bridge construction site near the tunnel, and taking into account the regional karst development and the particularity of the location of the solitary peak, a calculation model of the volume karst ratio is established, and the tunnel surrounding rock is preliminarily classified in combination with volume karst ratio, karst development form and scale, karst filling, groundwater runoff and karst cave stratification characteristics as the main calculation parameters. According to the existing tunnel excavation experience in karst area, the relationship between volume karst ratio and the proportion of tunnel surrounding rock classification is established, which can better control the project cost for the design, construction and construction units.