The flow characteristics during spillway energy dissipation in high-arch dams are complex and are significantly affected structural stability. To analyze the hydraulic properties and damage mechanisms involved, numerical simulations were performed using the RNG k-ε turbulence model and the VOF method for tracking the gas-liquid interface. The numerical results were compared with discharge capacity data from the hydropower station’s storage plan and operation schedule, which demonstrated high accuracy and minimal computational error. On this basis, the hydraulic behavior of the plunge pool under various operating modes, upstream/downstream water levels, sediment particle sizes, and sediment concentrations of sand-laden flow was systematically investigated. By analyzing simulated velocity and pressure distributions, as well as turbulent kinetic energy, the evolution of key hydraulic parameters and associated damage mechanisms under different operating conditions were revealed. The results show that the maximum impact pressure of the plunge pool occurs in the drop point area of the water tongue, and is increased with the increase of the number of flood discharge holes, and the increase rate is slowed down when multiple holes are in operation; the increase of water level difference between upstream and downstream leads to a significant increase in impact pressure, and sediment-laden flowfurther aggravates the risk of floor abrasion. The damage of hydraulic structures can be effectively protected by water diversion and sediment discharge. The distribution of turbulent kinetic energy is in good agreement with the actual abrasion area, which can be used as an important basis for abrasion risk assessment. The research results of this paper can provide theoretical support for the optimal design and safe operation of flood discharge and energy dissipation of high-arch dams, and have important practical significance for reducing the risk of structural damage and prolonging the service life of the project.