Taking the drainage design of a tunnel in Hefei City as an example, the selection of design parameters and the calculation process of tunnel drainage are expounded. The designed rainwater flow in the tunnel is 1 623.5 m3/h and the designed wastewater flow is 8 m3/h. The elevation relation among the tunnel, intersected road and existing river is analyzed. The hump of road and the water retaining wall of auxiliary road are designed to ensure the rainwater of surrounding roads not to flow into the tunnel. The tunnel rainwater, flushing wastewater and structural leakage water are collected by setting the transverse ditch at the road hump and the drainage side ditch at two sides of tunnel. The rainwater pumping house co-built with the tunnel is set below the lowest point of the tunnel. The rainwater and wastewater lifting pumps are set respectively in the pumping house to lift the collected rainwater and leakage water and discharge into the nearby rivers. The flushing wastewater is lifted and then discharged into the road sewage well. The discharge capacity of the drainage ditch is checked by SWMM model. It is verified that the width × depth = 400 mm × 450 mm drainage ditch can meet the drainage demand under the conditions of Chicago rain pattern, rainstorm return period of 50 a and rainfall duration of 2 h.