Abstract: Objective Odor issues in EMU（electric multiple units） toilets directly affect passenger comfort and satisfaction. Ammonia is one of the main sources of toilet odor. Different airflow organization methods influence the spatial distribution of ammonia. In response, it is necessary to analyze the impact of typical EMU ventilation system airflow organization on the emission and dispersion of toilet ammonia. Method A simulation analysis model is established based on the toilet of a certain EMU type. The parameter settings and simulation assumptions are introduced. The simulation examines the distribution of ammonia mass fraction under different airflow organization methods in the ventilation system, revealing the role and influence of ventilation system airflow organization on toilet air quality. Based on the simulation results, improvement strategies such as optimizing the layout of air supply and exhaust outlets and adjusting the supply-exhaust air volume ratio are proposed. Result ＆ Conclusion The arrangement of air supply, intake and exhaust outlets inside the toilet has a significant impact on the ammonia mass fraction. A well-designed airflow organization in the ventilation system can effectively reduce the ammonia concentration. The airflow configuration with air supplied from the toilet ceiling, exhausted from the lower part of the toilet, and fresh air introduced from the upper part of the door panel can effectively disperse ammonia emitted from the toilet bowl, facilitate ammonia discharge, and effectively reduce its diffusion toward the upper part of the toilet, thereby improving the air quality in EMU toilets.