Abstract: Objective In recent years, as the rail transit field advances toward faster, safer, greener, and more energy-efficient development, requirements for EMUs（electric multiple units）-a highly integrated complex system-are continuously increasing. Consequently, it is necessary to explore a new product development mode for EMU systems that better aligns with the contemporary demands, thereby achieving the ultimate goals of shorter research and development cycle, lower development costs, and higher product reliability. Method Taking the water supply and drainage sanitation subsystem of an EMU in China as example, the IPD（integrated product development） mode is applied to investigate train-level functional groups using this system. First, six train-level functional groups using water supply and drainage sanitation are identified. Then, with system requirements as the core, an architecture design is performed for the above functional groups to facilitate interactions among all relevant subsystems, thus connections between all inputs and outputs are identified. Finally, requirements are allocated to all subsystems. Result ＆ Conclusion The implementation of the IPD framework-as a new development mode, philosophy, and methodology-integrates all participating parties during project early decision-making phases, fully leveraging their respective strengths. This approach not only reduces costs for the new development products of EMU system, increases project returns, and enhances product quality, but also effectively ensures the smooth execution of projects.