It's been seven years since WWE superstar Chyna released her horrifying sex tape -- and TMZ has learned, she's making a triumphant return to the adult industry ... in an EXTREMELY graphic porno.

Vivid President Steve Hirsch tells TMZ, Chyna approached him months ago to breathe life into her XXX career -- demanding to work with the biggest male porn star in the business.

Steve did her one better ... and hooked her up with the TWO biggest male porn stars in the business -- Evan and Lee Stone -- and together, the threesome shot a gnarly skin flick ... tentatively called "Backdoor into Chyna."