The invention discloses a coating method, a coating device and a coating system. The coating method comprises: collecting a thickness data of a film on inner walls of a coating chamber; and processing the thickness data to obtain the thickness of the film on the inner walls of the coating chamber. With the coating method, the cleaning for the coating device gets smarter, the troublesome of artificially controlling the cleaning in the prior art is eliminated and thus the cleaning efficiency for the coating device is improved.