Weymouth beach came seventh. The top spot was taken by Rhossili Bay in Swansea, with surfers favourite Woolacombe Bay in Devon second.
The world's best beach award went to Rabbit Bay on the Italian island of Lampedusa. See the full list of winners here.
Bruce Grant-Braham, tourism champion for Dorset Local Enterprise Partnership, said: “Dorset has some of the best quality beaches, heritage and countryside in the UK, so it is fantastic that travellers recognise the unique qualities of this outstanding area.
“After being on show to the world during the Olympics, it is wonderful that this inspiring coastline is enjoying such popularity with visitors. We look forward to welcoming even more.”
Paul Dredge, vice chairman of the Poole Tourism Panel, said: “Poole's beaches are fantastic, so it is no surprise that Sandbanks features so strongly with travellers.
“The fabulous location and harbour create a unique and very special environment with a world class reputation for water sports and great events. Wonderful facilities, play areas and glorious views to be enjoyed all year round easily make Sandbanks one of the best beaches in the world.”
TripAdvisor spokeswoman Emma Shaw said: “These awards recognise the best beaches in the UK and beyond, according to those that really matter - travellers that have visited these beaches and given them the highest levels of praise.”