Artists on the bill for the fundraising show include Nickleback, Matthew Good, Corb Lund and Jann Arden.
Organizers expect to raise more than $2 million at the show, which will be hosted by comedian Brent Butt.
More than 30,000 tickets were sold — which organizers say will make the concert the biggest in the city's history.
The show starts at 6 p.m. MT with a pre-concert that started at 2: 30 p.m. already underway in the parking lot.
All the proceeds go to The Calgary Foundation's Flood Rebuilding Fund.
So far, funds have been used to support services offered by Inn from the Cold and the Alex Community Health Centre, said foundation official Kerry Longprey.
The foundation has already raised more than $4 million, not including the proceeds from the Aug. 4 Halo High Water Concert at the Jubilee Auditorium or tonight's concert.
A complete tally of the money raised should be available next week, Longprey said.