In view of the inconvenience of building vertical and inclined shafts due to factors such as construction conditions, geographical conditions and environmental assessment requirements for high-altitude tunnels and underwater tunnels, this paper proposes a parallel pilot tunnel-section longitudinal ventilation system. On the basis of the tunnel ventilation theory, the calculation formula of the design parameters suitable for the ventilation system is deduced. At the same time, combined with the tunnel ventilation design procedure, the paper gives the design process from the determination of the tunnel segment location, design air volume calculation, design parameters initial value calculation to pollutant concentration calibration. From the tunnel length limit and the required air volume, the paper initially analyzes the applicable conditions of the mixed ventilation method. Combined with the engineering case, the practical application scheme of mixed ventilation is given. Under the premise of not building a shaft, the scheme can solve the problem of fire escape by combining the centralized smoke exhaust channel, which has practical feasibility. The scheme solves the problem of escape of fire personnel under the premise of not building a shaft and combined with a centralized smoke exhaust channel. It has practical feasibility and is practical for crossing high altitude and the ventilation design of the cross-sea highway tunnel provides a new idea.