Abstract: The mechanical properties of wheel surface material change with the formation of polygonal wear on wheels of high-speed trains. Wheel samples with polygonal wear were obtained on a wheel/rail periodic wear simulator to study the change of surface material mechanical properties of polygonal wheels. Their Young’s modulus and hardness were obtained at different depths beneath the peaks and troughs of the worn surface using nano-indentation technique. Their yield stress and strain hardening index were determined by simulating the nano-indentation loading process combined with dimensional function method to obtain the material constitutive relations at different depths beneath the peaks and troughs of polygonal wear. The results show that different levels of plastic deformation occur at different locations in the wheel surface layers. Young’s modulus and hardness increase gradually from the bulk to the polygonal worn surface, and the increase at the troughs is greater than that at the peaks. The materials’ constitutive relations at the peaks and troughs of the worn surface differs greatly at difference locations, and the difference at the troughs is greater than that at the peaks.