Based on one-dimensional hydrodynamic-water quality coupled models and water environmental capacity models, this study analyzes the spatiotemporal distribution characteristics of ammonia nitrogen overflow pollution and water environmental capacity in urban rivers at a daily scale. Using the entropy weight method and fuzzy comprehensive evaluation method, a comprehensive regulation and control scheme for overflow pollution control is proposed, taking into account both environmental and economic benefits. The results show that at the daily scale, the peak mass concentration of ammonia nitrogen at river sections and the valley value of water environmental capacity exhibit an obvious lag effect in response to rainfall and pollutant discharge. Additionally, the water quality recovery time prolongs with increasing rainfall intensity. A spatial mismatch exists between overflow pollution distribution and water environmental capacity in rain-fed urban rivers:the midstream urban area serves as both the critical load zone for overflow pollution and the bottleneck zone for water environmental capacity, while the downstream area demonstrates strong pollution buffering and carrying capacity. Terminal storage measures can effectively reduce the peak mass concentration of ammonia nitrogen at river sections under light and moderate rainfall scenarios and maintain adequate water environmental capacity. For heavy rainfall scenarios, a combination of terminal storage and ecological water replenishment is required, and pollution load reduction near assessment sections yields the most direct improvement in water quality. Construction cost is a key factor restricting the implementation of overflow pollution control schemes. Under light and moderate rainfall, priority should be given to pollution load reduction, whereas under heavy rainfall, the pollution load reduction rate and ecological water replenishment volume need to be coordinately regulated to maximize environmental benefits under cost constraints.