To address the failure problem of the discharge valve in high-pressure reciprocating descaling pumps caused by cavitation damage and erosion wear, this study adopted a co-simulation approach using AMESim and Fluent, incorporating the Zwart-Gerber-Belamri cavitation model and the Generic erosion model to simulate the gas-liquid-solid multiphase flow field throughout its opening and closing processes.The results show that during the opening process, the discharge valve experiences a lag of approximately 0.003?s, while during the closing process, the lag is about 0.002?s. These lags induce pressure impacts, sudden flow changes, and backflow. Erosion wear primarily concentrates on the flow-passing surface and the bottom end face of the valve core. Backflow during the closing stage causes secondary erosion, shifting the wear zone to the flow-passing surface. Cavitation damage is mainly focused on the flow-passing surface and is significantly aggravated by backflow during the closing process. The simulated “T”-shaped erosion notch and “honeycomb-like” cavitation spalling morphology are consistent with actual failure patterns, confirming that valve core failure results from the combined action of cavitation and erosion. This research can provide theoretical basis and practical guidance for the reliability design of discharge valves in high-pressure reciprocating descaling pumps.