The list, drawn up by the Foreign and Commonwealth Office (FCO), includes Iraqi-born Zaha Hadid and husband-and-wife duo Marks Barfield. Both practices will be working with Arup.
Each team will now work up concept ideas and the six designs will feature in public exhibitions to be held in London and Shanghai simultaneously.
The £10 million pavilion - part of the World Expo's overarching theme of 'Better City, Better Life' - will have to handle up to 40,000 visitors a day over six months.
The pavilion will showcase Britain's culture, sport, media, education and business, as well as highlighting and promoting policies and technologies in low-carbon urban developments.
Malcolm Reading, who is managing the competition for the FCO and is acting as design adviser, said: 'This is a rich and distinctive shortlist. These are very creative teams, drawn from a longlist of 47 entries.
'The response was fantastic and reflects the widespread interest from the design community in this unique project. We want this pavilion to be amongst the top ten exhibits at Expo 2010,' he added.