The heart of the screw drill (also called positive displacement motor, PDM) is the rotor, it decides the work efficiency and performance of the screw drill. In this paper, the influence of different slurry solid content and additive on rotor surface wear was studied, and a special testing set was made to stimulate the rotor surface wearing rule under real downhole working conditions. The rotor wear regularity under different mud conditions was explored, which was further studied. It is found that the solid particle and salty additives are the main reasons for hard chromium coating damage and identifies that the main form of hard chromium coating damage is corrosive wear. Some suggestions are presented to the rotor manufacturing process and the application.