Abstract: The ongoing destruction and degradation of wetlands represent a critical ecological and environmental challenge confronting nations globally. As a fundamental strategy for wetland restoration, ecological water replenishment plays a pivotal role in sustaining essential wetland functions. Consequently, accurately assessing ecological water requirements becomes imperative, necessitating consideration of the diverse ecological services and environmental functions provided by specific wetlands. Physical habitat simulation offers a robust methodological approach by quantifying how target protected species respond to alterations in their environment. This technique enables the precise determination of optimal ecological water requirements needed to support the survival and viability of these focal species within wetland ecosystems. This study addresses this need through a focused investigation of the Qilihai Wetland in Tianjin. We developed and rigorously validated a hydrodynamic model to simulate water movement and distribution within this system. Selecting the endangered Siberian Crane (Grus leucogeranus) as our target indicator species, we employed this model to calculate the area of suitable foraging habitat available across a gradient of water levels. Subsequently, we derived the ecological water requirement for the wetland based on the insights gained from these hydrodynamic simulations. Our results demonstrate a clear, non-linear relationship between water level and habitat suitability for Grus leucogeranus. Specifically, the area of suitable crane habitat exhibited a distinct peak, initially increasing with rising water levels before subsequently declining. The maximum suitable foraging area, reaching 1.51 km², was achieved at a water elevation of −3.52 m above sea level. This optimal habitat area constituted 71.99% of the total study region. Based on this critical water level threshold and accounting for necessary hydrological processes, the annual ecological water requirement for the Qilihai Wetland was calculated to be 313.27×10⁴ m³. To consistently maintain habitat conditions that maximize the suitable area for Grus leucogeranus, proactive water management is essential. This involves strategically implementing water replenishment or controlled withdrawal measures, dynamically adjusted in response to prevailing monthly weather conditions and associated evapotranspiration rates.