TiN/CrN multilayer coating was deposited on AZ91D magnesium alloy by pulsed bias cathodic arc PVD process. Effects of the coating on wear and corrosion behaviours of magnesium alloy were investigated. The stick-tearing for adhesion evaluation, nanoindentation for hardness measurement, ball-on-disc testing for wear tests, and potentiodynamic polarization for corrosion tests were used. The results show that the friction coefficient is decreased and the wear resistance is improved remarkably by TiN/CrN multilayer coating on AZ91D magnesium alloy. The corrosion resistance of the alloy is increased at a certain degree.