The pavilion has already been given a nickname - the dandelion - which is a Chinese good luck symbol.
The theme of Shanghai Expo is Better City, Better Life. This inspired British designer Thomas Heatherwick to create a park in which people could relax in one of the world's busiest urban spaces.
A key part of the UK pavilion is a 'Seed Cathedral', which sits at the centre of the Heatherwick-designed parkland site.
Thomas Heatherwick said: "It has been a tremendous achievement of the team to deliver such a complex structure. I am excited that the Seed Cathedral is now complete and I look forward to the millions of visitors to the Expo enjoying the space."
The Seed Cathedral is 20 metres in height, formed from 60,000 slender transparent rods, each 7.5 metres long and each encasing one or more seeds at its tip. During the day, they act as optic fibres and draw daylight inwards to illuminate the interior. At night, light sources inside each rod allow the whole structure to glow. As the wind moves past, the building and its optic fibres gently move.
The seeds have been sourced from China's Kunming Institute of Botany, which is part of the Royal Botanic Gardens, Kew's Millennium Seed Bank partnership.
Professor Stephen Hopper, director of the Royal Botanic Gardens, Kew said: "We are delighted to be involved in the UK Pavilion - especially as 2010 is the International Year of Biodiversity. Seeds stored in Kew's Millennium Seed Bank in the UK, and in our partners' seed banks around the world, have the potential to enable human innovation, adaptation and resilience; helping current and future generations to lead better lives."
70m people are expected to visit the Shanghai Expo, which opens to the public on 1 May for six months.