The multi-principal AlCrNbSiTiON oxynitride coatings were deposited by pulsed arc ion plating under different oxygen flow. The structure and mechanical properties of the coatings were systematically investigated. The surface of all coatings is smooth and flat. The cross section is compact and smooth. The coatings transform from FCC solid solution crystal structure with (200) preferred orientation to amorphous/nanocrystalline nanocomposite structure with increasing oxygen flow. Upon increasing oxygen flow from 0 to 150 SCCM, their hardness decreases from 43.4 to 15.6 GPa. The hardness of the coatings increases to 26.4 GPa with increasing oxygen flow again. The Cr2O3 oxides are formed on the surface of the coatings during the friction process.