The use of flip bucket with small slope in aeration facilities along high-velocity flood discharging tunnels can effectively improve the flow conditions within tunnels, but it is difficult to guarantee the aeration effect under large variations of head. Based on the Kashi Hydropower Station, this paper adopts a hydraulic model test to study the hydraulic characteristics of the aeration facilities in flood discharging tunnel under various heads, and analyzes the adaptability of the flip bucket with small slope configuration. The study shows that when the head is 70m or above, the cavity of the flip bucket with small slope without backwater, and has good aeration effect; when the water head is between 25m and 70m, there is varying degrees of backwater in the air cavity, and the aeration effect slightly decreases with the decrease of head. The average reduction of effective air cavity length, ventilation hole airflow, and aeration concentration are 20.4%, 13.4%, and 12.1% respectively, indicating that the aeration facilities with flip bucket with small slope have a wide range of water head adaptability; when the head is below 25m, the aeration effect is significantly reduced, and even the entire cavity is filled with backwater, without aeration mitigation cavitation effect.