Cowell says, "I always said it had to be someone who wasn't better looking than me and they achieved it."
He poked fun at Tyler before collecting the Founders Awards at the International Emmy Awards in New York on Monday night.
Cowell said the Aerosmith frontman seems like a nice guy, and Randy Jackson told him they were having a lot of fun.
He believes Tyler can adequately fill his shoes, but stopped short of saying the rock star would damage his credibility being on the show.
Cowell says the role of judge is something that Tyler wants to do and that "it's a fun job. You got to take it like that. You can't take it too seriously."