Abstract: In order to deal with the disadvantages of large local resistance and wind loss in the large-angle bends of the tunnel with traditional ducted ventilation, taking the An′ ding tunnel on Yumo railway as the engineering background, an air cabin ventilation system for tunnel construction is designed by the method of numerical simulation. Based on the fan efficiency, total wind pressure and the smoothness of the air flow in the air cabin, the optimal dimension of air cabin is determined by using controlled variable method. The calculation results show that the ventilation efficiency is high, the air cabin requires less material which is more economical and practical, the air pressure of the four fans is balanced, the fans are well coordinated, and the air flow field in the air cabin is uniform and stable when four SDF No. 12.5 axial fans are equipped to supply air to each working face of the tunnel and the dimensions of the air cabin is 18 m long and 4.5 m high and the space between fan centers is 8 m.