Pluvial floods increasingly threaten emergency medical systems (EMS) by disrupting road networks. Previous studies have examined flood impacts on roads and EMS separately, neglecting population distribution. This study evaluates EMS accessibility loss and flood-induced medical deserts under pluvial floods in Mentougou New Town. Flood inundation under 10-, 20-, 50-, and 100-year return periods is simulated using MIKE FLOOD. The the simulated water depths are used to adjust travel speeds and identify interrupted road segments. Based on the resulting travel-time matrices, 8-min service areas are calculated and overlaid with high-resolution population data. The results reveal that flood risk exhibits nonlinear growth characteristics, with the 50-year return period rainfall event representing a critical threshold. Under the 50-year event, several key roads begin to fail, and the EMS coverage area contracts sharply. Under the 100-year event, large flood-induced medical deserts appear in old urban districts, high-density residential communities, and peripheral industrial zones. These areas form where road disruption, concentrated population, and limited alternative access overlap. The findings demonstrate that road-network failure and population exposure must be assessed jointly when evaluating flood impacts on EMS, supporting emergency planning, critical road protection, and resilient medical resource allocation in flood-prone cities.