The work aims to study corrosion behavior of hard chromium plating on surface of screw drill in high temperature and high pressure chloride ion environment. The hard chromium plating on surface of screw drill was corroded and tested by simulating downhole environment of screw drill with high temperature and high pressure reactor. Effects of temperature, pressure and chloride ion concentration on corrosion state of hard chromium plating were studied in the method of orthogonal experiment. Electrochemical parameters and corrosion characteristics of hard chromium plating were studied in the methods of dynamic potential scanning and weight loss corrosion. Changes in microstructure and surface composition of the corroded plating were analyzed by using scanning electron microscopy and EDS. The most important factor affecting corrosion rate of the hard chromium plating was the chloride ion concentration, followed by the temperature and pressure. The most serious corrosion depth of the was 0.8925 mm/a, and the maximum corrosion rate was 1.9026 g/(m2?h). The corrosion rate decreased with increase of chloride concentration, and increased with the increase of temperature and pressure. It is inferred that the most severe corrosion of the hard chromium plating occurs nearly provided with the temperature of 180 ℃, pressure of 15 MPa and NaCl mass concentration of 30 g/L. Chloride ion is the main factor affecting corrosion rate of the chromium plating because the chloride ion preferentially initiated pitting nuclei in the sensitive position (the weak point of passive film, such as crack). Under the effect of occluded corrosion cell catalysis, pitting corrosion continuously occurs on the plating, cracks are widened, and ultimately leading to peeling of local plating, thus affecting overall protective properties of the plating.