There are two construction methods for subsea tunnels. One is to drill holes in the seabed with a drilling rig under the seabed. The other is to lay the prepared reinforced concrete pipeline on the seabed ground and fix it on the seabed with a special steel frame. Now some people have put forward the idea of using buoyancy to build suspended submarine pipelines.

The longest undersea tunnel built in the world is the Qingxin Tunnel in Japan. The total length is 53.85 kilometers, including 23 kilometers under the sea. The cross-harbour tunnel connecting the European continent and Britain in the English Channel is 53 kilometers long, of which 38 kilometers pass through the 40-meter-deep rock stratum. The tunnel started on 1987 and was officially opened to traffic on 1993. The Japan-Korea tunnel started on 1985, with a total length of 250 kilometers, a height of 4.5 meters and a width of 5 meters, and will pass at a depth of 80-300 meters under the sea. The project was excavated from both Japan and South Korea.