The fans have been camping out since last night in the hope of catching a glimpse of stars Emma Watson, 21, Rupert Grint, 22 and 21-year-old Daniel Radcliffe on Thursday.
Lots of tents and sleeping bags are lining the ground in London's Trafalgar Square - where the actors will greet fans on the red carpet.
They will then head to Leicester Square for the screening of Harry Potter And The Deathly Hallows Part 2.
The movie is set to be released on July 15 and marks the end of the eight-part series based on JK Rowling's hit books.