24 January 2014 Last updated at 08:29 GMT
He's heading to the International Space Station for a mission next year.
Major Peake is training at the European Astronaut Centre in Germany, where he's using a pool to try and experience what it's like to work in zero gravity.
Watch this clip of Major Tim Peake talking underwater!
The UK's first official astronaut, Major Tim Peake, has been training underwater to prepare him for space.