The invention discloses an automatic oil spraying device which comprises a closed oil spraying room, a fog spraying system, an oil recycling system and a control system. The fog spraying system comprises a main air source, a pressurizing mechanism, an oil drum, an electromagnetic valve and fog spraying valves, wherein the main air source is connected with the pressurizing mechanism, and the oil drum, the pressurizing mechanism and the fog spraying valves are sequentially connected through oil pipes. The electromagnetic valve comprises an air inlet, a first air outlet and a second air outlet, wherein the air inlet is connected with the main air source through a pipe, the first air outlet is connected with the fog spraying valves through a driving air source pipe, and the second air outlet is connected with the fog spraying valves through an atomization air source pipe. The driving air source pipe and the atomization air source pipe are provided with a first pressure adjustment mechanism and a second pressure adjustment mechanism respectively. The electromagnetic valve and the oil recycling system are respectively connected with the control system, and the oil recycling system is connected with the closed oil spraying room. The invention further discloses an automatic oil spraying method achieved through the automatic oil spraying device. By means of the automatic oil spraying device and the automatic oil spraying method, rapid and safe rust prevention processing on a large number of plates can be achieved, operation risks to persons are reduced, and waste oil can be recycled.