Abstract: The swirling-blocking composite internal energy dissipator is a novel energy dissipator which is applicable to the flood discharge and energy dissipation of high dams. In order to analyze its application to the flood discharge and energy dissipation of dams with ultra-high water head, its hydraulic characteristics under the condition of 200 m water head are studied by means of physical model test and numerical simulation. The results show that with the application of this novel dissipator, the discharge is 1 547 m~3/s, which is slightly larger than the design value but can still meet the discharge requirements. There is a stable swirling flow in the cavity, and the diameter of the cavity in the swirling section is about 6-7 meters, with a swirling angle of about 60°. In the swirling section, the wall pressure is about 110×9.8 kPa, and the maximum point velocity is about 45 m/s. There is a low frequency pulsation between the swirling flow generator and the swirling section, which is 0.050 to 0.274 Hz, and the cavitation number is greater than 1.2, indicating that the discharge operation is safe. The minimum instantaneous negative pressure at the end of the blocking diffusion section is-3.81×9.8 kPa, and the cavitation number of the flow is small; however, the possibility of cavitation would be greatly reduced due to the high aeration rate of the flow. The dominant frequency of the flow at the end of the diffusion section is 46.99 Hz and the total energy dissipation rate is as high as 82.1 %. The research results can provide some reference for the application of the composite energy dissipator to the flood discharge and energy dissipation of dams with high water head.