ObjectiveAs a key parameter in the simulation study of ecosystem water cycle process, rapid dynamic simulation of leaf area index (LAI) can solve the limitation that the coupled soil water-vapor-heat-air model STEMMUS (simultaneous transfer of energy, mass and momentum in unsaturated soil) can only use fixed or measured LAI as an input parameter.MethodsIn this study, the "plant leaf area development sub-module" in EPIC model was coupled with the STEMMUS model, and the model was calibrated and validated using the measured transpiration of apple trees, soil moisture and soil temperature data under the growth conditions of apple trees in the mountain apple experimental demonstration base of Zizhou County in 2019 and 2020, so as to evaluate the applicability of the coupled model on the Loess Plateau.ResultsBy optimizing the plant growth parameters, the coupled leaf area development sub-module of the STEMMUS model significantly improved the simulation accuracy of the transpiration and water consumption process of apple trees, with the normalized root mean square error (NRMSE) of the calibration and validation years decreasing from 40.2% and 61.9% in the Original model to 30.0% and 33.2% in the coupled model, respectively, and the mean absolute error (MAE) decreasing from 0.52 and 0.64 mm/d to 0.42 and 0.38 mm/d, respectively. Meanwhile, the coupled model could better simulate the soil hydrothermal dynamic processes in apple orchards, and the NRMSE of simulated soil water content and soil temperature during the calibrated period and validation period ranged from 1.4% to 32.9% and 2.9% to 9.5%, respectively, and the MAE ranged from 0.13 to 4.26 cm³/cm³ and 0.34 to 1.49 ℃, respectively.ConclusionThe high agreement between the simulated and measured values indicates that the coupled model can accurately describe the dynamic growth process of apple tree leaf area and the ecohydrological process of orchard on the Loess Plateau, and this study can provide technical support for the research of the ecohydrological process of orchard in loess area.