Abstract: As for the design and construction of highway tunnel,accurate surrounding rock classification is the pre? requisite for evaluating stability and guaranteeing safety of tunnel construction and operation.The current surrounding rock classification method specified for the highway tunnel is adopted in the construction of a highway tunnel in nearly horizontal red-bed stratum, and it is found that there is a big difference between the classification results and the actual results reflected by self-stability of surrounding rocks. Based on an analysis of the engineering characteristics of the surrounding rocks of tunnels in nearly horizontal red-bed stratum, it analyzes the causes and tries to correct the correction factor of underground water effect, and the stratum thickness effect factor is added, which makes the current classification method of surrounding rocks be suitable for the highway tunnel in nearly horizontal redbed stratum. The applicability of classification indexes is preliminary verified by practical engineering case, and the results obtained by the corrected classification indexes of surrounding rock meet the requirements for the stability evaluation of surrounding rocks during the design and construction of the highway tunnel in nearly horizontal redbed stratum.