Using the WRF model, this study investigates the impact mechanisms of surface evaporation—including three types (direct soil evaporation, canopy evaporation, and vegetation transpiration), evaporation rates, and re-evaporation of prior precipitation on the “08·24” heavy rainfall event in the Three-River-Headwater Region of Tibet Plateau. Results demonstrate that eliminating direct soil evaporation significantly reduces afternoon scattered precipitation during the development stage (due to suppressed moisture flux under peak solar radiation), while suppressing vegetation transpiration decreases precipitation across all stages (via disrupted daytime moisture supply from stomatal conductance). Canopy evaporation primarily affects precipitation during the mature and dissipation stages (by rapidly releasing intercepted water within hours post-precipitation under daytime energy supply). Increasing evaporation rates enhances precipitation (maximum more than 40 % during development). Crucially, re-evaporation of former precipitation sustains rainfall in mature/dissipation stages (through moisture recycling of precipitation during the development stage). Sensitivity experiments quantify stage-specific conversions in the water vapor-hydrometeor-precipitation chain and establish a novel conceptual model of precipitation-evaporation feedback, providing the first mechanistic insights into heterogeneous evaporation controls on extreme rainfall in high-altitude “water towers”.