A tunnel proposal named SMART is put forward to solve the problem of flood discharge in raining seasons and to mitigate the traffic congestions in downtown area of Kuala Lumpur. The tunnel, with 9.7 km length, has an internal diameter of 11.8 m. In nonflood seasons, the 3 kmlong central section of the tunnel is also used as motorway tunnel with 4 lanes in bidirections. In the paper, the critical issues involved in the course of proposal conceive, project design and construction are briefly presented, which can provide reference for similar projects in the future.