The invention discloses a thin liquid film corrosion testing method capable of controlling the thickness of a liquid film automatically. A device adopted in the method comprises an iron support, a micrometer caliper I, a micrometer caliper II, a probe I corresponding to the micrometer caliper I, and a probe II corresponding to the micrometer caliper II. A liquid storage tank is connected with an electrolytic bath through an electromagnetic valve. Before a test is started, circuit connection is conducted firstly, and a universal meter is connected to a circuit where the micrometer caliper I and a working electrode are located; the micrometer caliper II and a platinum electrode are connected with a wiring port of the electromagnetic valve to form a circuit; then the thickness of the liquid film is set through the probe I and the probe II. When the test is conducted formally, automatic liquid replenishment can be achieved through opening and closing of the electromagnetic valve. By the adoption of the method, the thin liquid film can be controlled automatically, conveniently and accurately to be maintained at a certain thickness within a certain range, the thickness can be adjusted conveniently, metal corrosion electrochemical data acquisition at a certain liquid film thickness is achieved, and then research on metal corrosion mechanisms at different film thicknesses can be facilitated.