There are plenty of pipes to be arranged in subway station platform. Optimizing the air-conditioning system ducts is especially important because of its large size. Due to the location of stairs and the size of ducts, the platform exhaust ducts of a Shanghai subway station were laid out within the range from the stair to the end of the platform which probably can’t exhaust smoke effectively in fire. In reconstruction plan, air supply ducts and discharge ducts are connected and valves are added. Air supply pipe can be changed into discharge duct by controlling the valves. The smoke extraction performances of the original plan and the reconstruction plan are analyzed with the CFD numerical simulation. The results show that the reconstruction plan can make up the shortcoming of the original plan and contribute to the layout of pipes in new platform.