"stage floor" is correct and usable in written English.
You can use it when referring to the floor of a theater stage. For example, "The stage floor was littered with props and costumes from the previous show."
The stage floor has been painted black.
The stage floor occasionally glowed with squares of light.
Screwing or nailing anything into the stage floor, walls or ceiling is not permitted.
The vertiginous downward curve of the stage floor gives the ballroom scenes an overwrought surreal quality.
Sets were changed by sliding them in grooves in the stage floor and overhead.
Minutes ago, several of them had lain on the stage floor in less than perfect health.
He threaded his way through his audience and sat down on the stage floor.
When she finished, a hundred-foot-tall puppet of Voldemort rose from the stage floor.
Grooves were made in the stage floor to support the flats and facilitate their movement.
"The bottom edge would have dragged on the stage floor," Mr. Branchick said.
The stage floor, furnished with just a low riser, had been painted battleship gray.
