The rider, troupe owner Ken Fox, was taken to Derriford Hospital, Plymouth after falling from the top of the cylindrical track.
An eyewitness told BBC News: "There was an air of panic with people screaming and running out of the tent."
Mr Fox, from Cambridge, was treated for bumps, bruises and scratches.
Emergency services remain on the scene at the showground in Wadebridge speaking to witnesses.
On Facebook, Ken Fox Wall of Death said in response to concerns for the rider: "Ken Fox is safe and well just a bit bashed about."
Devon and Cornwall Police say nobody else was injured in the accident.
The wall of death is a motorcycle show in which stuntmen ride at speed around a vertical track performing tricks and stunts on 1920 Indian Scout bikes.
The Ken Fox Wall of Death troupe has been featured in music video and on television, including the BBC One idents showing stunt riders going round in a circle.
The eyewitness said the rider fell from the top of the wall on to his head but he could not see why he fell.
People outside said they heard a huge bang and that they felt the earth shake.
A motorcycle stuntman was airlifted to hospital after an accident during a "wall of death" performance at the Royal Cornwall Show.