Ten fire engines were sent to the blaze, which broke out in an unoccupied building at the site.
The college, which closed in 2014, is due to reopen to students this September.
A spokesman for the college said: "A small fire at Haywards Heath College is now contained.
"We can confirm that there were no staff or students on site and there are no reported injuries.
"There is now an investigation underway working with West Sussex Fire & Rescue Service.
"We understand that the fire started in a small dance pod.
"We continue to work closely with the site owner, the Department of Education and the contractors, Kier, who were carrying out work on the site ahead of the opening in September 2020."
The spokesman confirmed that a college open day, due to take place on February 11, will still go ahead.