The nitrided layer was prepared on the AlCoCrFeNi high-entropy alloy by plasma nitriding. The microstructure and tribological property of the nitrided layer and as-cast high-entropy alloy were studied at dry sliding condition, deionized water and the add rain, respectively, The results showed that the hardness of the nitrided high-entropy alloy was increased from HV 522 of as-cast high-entropy alloy to HV 720 of nitrided high-entropy alloy due to the presence of hard phases and solid-solution strengthening. In addition, the wear resistance of the nitride layer was superior to that of the as-cast alloy in the same condition. Moreover, the wear rate of nitride layer obtained a minimum of 2.8 x 10(-5)mm(3)/(Nm)in the acid rain due to the oxidation film, nitrided layer and the lubrication action in solution. The dominant wear mechanism of the as-cast alloys and the nitrided HEM in the acid rain was abrasive wear, oxidative wear and corrosive wear. However, the main wear mechanism of the as-cast alloys and the nitrided HEM in air and deionized water was abrasive wear, adhesive wear and oxidative wear. (C) 2017 Elsevier B.V. All rights reserved.