The stunning Quidditch scenes were shot at the castle.
A spokesperson told CBBC Newsround Online that visitor numbers have more than doubled compared to last year.
He added: "What we've seen is a lot more enquiries from families all over the world - from Malaysia, Australia - saying their children are keen to visit because of Harry".
He reckons even though it's still the same old pile of stones as it has always been, there's a new magical feeling to the castle.
Hundreds of children have been choosing to go the castle to take their photo on the same spot Harry stood.
Flocking to Gloucester!