Abstract: By means of chemical composition analysis, macro and micro fracture analysis, metallographic analysis, hardness test and so on, the cracking reasons of a metro rail at the rail waist were analyzed. The results show that the poor weld bead surface quality, the existence of net ferrite in the weld center and the excessive non-metallic inclusions in the base metal, caused brittle cracking of the rail at the rail waist under the action of external stress. Finally, the improvement measures were put forward according to the causes of the rail cracking.