This paper describes a study of the corrosion behavior of Cr-modified steel reinforcement exposed at marine splash zone for a period of two years. The corrosion behavior was analyzed by the weight loss method, optical and electron microscopy, and X-ray photoelectron spectroscopy. The Cr-modified reinforcement exhibited high corrosion resistance in the actual marine environment. The protection mechanism of the Cr-modified reinforcement at the corrosion propagation stage was that Cr improved the protective quality and buffering ability of the rust layer against aggressive species, by increasing the Fe2+ and OH− content within the iron oxides and improving the compact degree of the rust layer.