In this study, three-dimensional point cloud data of lining surfaces from three typical tunnels is collected, and the weighted average deviation is introduced as a quantitative indicator for surface flatness. The influence of shotcrete lining surface flatness factors—roughness element height, tunnel diameter, and roughness element spacing—on frictional resistance coefficient in tunnel ventilation is investigated. The results of the study indicate the following: (1) The surface flatness factors effectively characterize the surface flatness of the shotcrete lining, with measured surface flatness values concentrated in the range of 0.4－2.2, consistent with actual engineering conditions. (2) The results of the numerical simulation analysis demonstrate a marked increase in the frictional resistance coefficient with the height of the roughness elements, a gradual decrease with increasing tunnel cross-sectional diameter, and a corresponding decrease with increasing roughness element spacing. (3) Following a systematic comparison and analysis of the empirical calculation formula for the frictional resistance coefficient with the numerical simulation results, a correction factor of 1.193 is determined. The validation process has demonstrated that the revised calculation formula aligns closely with measured data, thereby significantly reducing the discrepancy between theoretical predictions and engineering practice. (4) Based on the recommended value of 0.02 for the frictional resistance coefficient of concrete tunnel walls from the Guidelines for Ventilation Design of Highway Tunnels. Additional values for the average wall roughness height and corresponding surface roughness for typical tunnel diameters are hereby proposed.