The invention relates to a plane spraying device which comprises a flow split unit, a filtering unit, a spray head seat unit and a jet unit which are sequentially connected and internally provided with spraying material channels and gas channels, wherein the spraying material channels and the gas channels in the flow split unit, the filtering unit, the spray head seat unit and the jet unit are respectively, sequentially and correspondingly sealed and communicated to form a spraying material channel for spraying materials to flow through and a gas channel for compressed air used for dispersingthe spraying materials to flow through; the inlet of the spraying material channel and the inlet of the gas channel of the flow split unit are respectively connected with an external spraying material supply device and a compressed air supply device; and the tail ends of the spraying material channel and the gas channel of the jet unit are respectively provided with a spraying material jet port and a gas jet port. The invention also provides a plane spraying method based on the device. Through adopting the device and the method, the smoothness and the tightness of the spraying material channels can be conveniently controlled, and spraying materials of different colors and/or chemical properties are matched so as to achieve various spraying effects.