Spring ecological water requirement for the fishes in the Yellow River Estuary should meet the needs of the habitat and spawning ground of freshwater fishes, channel of migratory fishes, and spawning ground of offshore migratory fishes. According to the living habit of fishes, the time of runoff propagation, the mixing time of fresh water and salt water, and the discharge feature since the operation of the Xiaolangdi Reservoir, key attention should be paid to the water requirement from March to May. A minimum ecological flow discharge of 240 m³/s is needed according to the living habit of fishes and the continuity of the migration channel. A flow discharge pulse with a peak of 890 m³/s, lasting for 8d in the middle stage of April is also needed considering the pulse characteristics in nature period. In this condition, the runoff in spring is 21. 6×10⁸ m³, satisfying the requirement of 21×10⁸ m³ for the low salt spawning condition of offshore migratory fishes. The mean annual spring runoff is 21×10⁸ m³ since the operation of the Xiaolangdi Reservoir. It is of great feasibility to satisfy the fish ecological water requirement by optimizing the annual or the interannual operation modes.