Abstract: Underframe structure is the most important and most difficult part in urban rail transit vehicle body structure design. Based on the NYCT Qualification Project, metro vehicle underframe structure design scheme and key points formulated from ASME RT\|2—2014 Safety Standard for Structural Requirements for Heavy Rail Transit Vehicles are expounded from the perspectives of end underframe energy absorption structure, underframe side beam, underframe middle beam and the whole structure. The mechanical properties and weld standard of the applied carbon steel and stainless steel material are described, and static strength numerical computation, energy absorption numerical computation and relative experimental verification are carried out on underframe steel structure. Results show that the static strength value, stiffness and impact energy absorption value of underframe structure all meet the needs of vehicle design.