Through the observation and analysis of the spillway and the downstream discharge flow state, it is revealed that the protruding mouth on the right bank causes the mainstream to fold and reduce the water passage area of the river, and at the same time, the thickness of the downstream water cushion is not enough, and the steep longitudinal slope and lateral height difference of the river channel are large. Insufficient energy accumulation and energy dissipation of the water flow formed is the main reason for the scour damage in the downstream of the spillway of Hualiangting Reservoir during the floods in 2016 and 2020. The control measures to reduce the scour and damage downstream of the spillway are put forward mainly by reinforcement protection, smooth flow state and secondary energy dissipation, which can provide a reference for the downstream regulation and reinforcement design of similar reservoir spillways.