In this paper, an optical fiber corrosion sensor with stepped metal film was designed and fabricated. The principle of the optical fiber sensor for corrosion monitoring was analyzed. The stepped metal film was prepared by magnetron sputtering and electroplating on the core of multimode optical fiber with cladding removed. The optical performance of the sensor with different steps was investigated by optical power measuring. The result showed that a stepped metal film on optical fiber could enhance the properties of sensor, and the detective range was enlarged.