Safety issues caused by cavitation erosion of flood discharge and energy dissipation structures (FDEDS) are becoming increasingly prominent due to the high head, high power, and high flow velocity of high dams. Existing research primarily focuses on single or limited cavitation bubbles, making it difficult to scale simulations to match the macroscopic experimental conditions. In this study, an equivalent multiscale modeling approach for cavitation erosion loading is proposed. Based on the micro-jet theory and the differential method, equivalent models for point and micro-line loading were first developed, and then extended to line and plane loading by incorporating the spatial distribution characteristics of cavitation bubble groups. To address the challenge of determining key parameters in the equivalent models caused by the stochastic nature of ultrasonic cavitation bubbles, an inversion method for loading parameters is established. This has led to the development of a comprehensive multi-scale equivalent simulation method for cavitation erosion. The validation analysis demonstrated that the proposed simulation method achieved high accuracy, with results closely matching the experimental data. These findings provide a reliable technical foundation for the safety evaluation of cavitation erosion in the FDEDS of high dams.