To obtain the reasonable parameters of a smoke exhaust shaft in a tunnel under different longitudinal slope conditions, the temperature, flow velocity, and smoke exhaust efficiency of the tunnel were taken as indexes, and the numerical model was established by using fire dynamics simulator (FDS) software to study the influence of the longitudinal slope of the tunnel, shaft width, and shaft length on the ventilation and smoke exhaust in case of a fire. The results show that under the longitudinal slope conditions, with the increase in the shaft width and length, the maximum temperature in the tunnel decreases, and the smoke exhaust efficiency of the shaft increases. However, the influence of the shaft width on the maximum temperature and smoke exhaust efficiency is greater than that of the shaft length. There is a correlation between the longitudinal slope of the tunnel and the shaft width. When the shaft width is not greater than 4 m, the increase in the longitudinal slope can effectively reduce the temperature of the vault above the fire source. When the shaft width reaches 5 m, the increase in the longitudinal slope improves the smoke exhaust efficiency. In the positive slope direction, the increase in the longitudinal slope makes the flue gas move faster. Based on the research results and industry norms, this study suggests that the size of the shaft be appropriately increased under the premise of structural safety and the influence of the longitudinal slope of the tunnel be considered.