The difference between ordinary tunnels and tunnel groups around the world is analyzed. The factors affecting the definition of tunnel groups are fully considered, including ventilation, lighting, fire safety, traffic safety, driver′s visual characteristics, and provisions in the Technical Guidelines for Quality Upgrade of Highway Tunnels. Then, the analytic hierarchy process is employed to gauge the importance of these factors. Moreover, the weight of each factor is calculated, and the defined distance of the when the design speed is 80 km/h, then lighting highway tunnel group is obtained. The results show the following: (1) The defined distances of tunnel groups corresponding to ventilation and firefighting are 400 m; when the design speed is 80 km/h, the defined distances of tunnel groups corresponding to lighting, traffic safety, driver′s visual characteristics, and technical guidance are 300、180、480, and 130 m, respectively. (2) By considering various factors, it is concluded that the defined distances of the tunnel group are 300, 350, and 400 m corresponding to design speeds of 80, 100, and 120 km/h, respectively.