Axle is a critical component of the train bogie. Surface defects that cause axle failures include corrosion, fretting wear and flying ballast impact damage. Surface integrity of axles can be improved by surface hardening to inhibit the initiation of surface cracks and slow down the propagation of surface cracks. As a result, the fatigue strength of axles is raised and the remaining life is extended. Surface hardening techniques of axles used in general speed and high-speed trains home and abroad including rolling, shot peening and induction hardening and their hardening mechanisms are summarized in this paper. Physical strengthening methods such as shot peening and rolling draw on plastic deformation strengthening and impart of residual compressive stress. Surface induction hardening improves the surface strength of axles by martensitic transformation and introduction of residual compressive stress. A comprehensive overview on the research and application of the above three axle surface hardening techniques in current axle manufacturing is given. Wherein, deep rolling is the dominant surface hardening technique for axles and surface induction hardening is utilized in small percent of high-speed train axles, while shot peening is less employed in axles manufacturing. Finally, the advantages and disadvantages of three axle surface hardening techniques are compared from perspective of economy and safety. The hardening depth of shot peening is not sufficient to prolong axle remaining life. From the point of hardening depth and residual stress magnitude, the hardening scheme of medium carbon steel axles is superior to that of alloy steel axles. Damage tolerance-based assessment provides guidance to the study and utilization of axle surface hardening techniques in the future.