A vehicle resin back door installation method includes: a vehicle body-side positioning step of attaching first positioning jigs to a vehicle body, and forming first sloping surfaces; a back door-side positioning step of attaching second positioning jigs to a back door, and forming second sloping surfaces; a temporary placing step of bringing the second sloping surfaces into contact with the first sloping surfaces, at the same time temporarily placing the back door on the vehicle body, and centering the back door in the vehicle width direction with respect to the vehicle body; an attaching step of attaching the back door to the vehicle body; and a detaching step of detaching the first positioning jigs from the vehicle body and detaching the second positioning jigs from the back door.