Evapotranspiration, as an important component of the water cycle on the Qinghai-Tibet Plateau (QTP), has long been a hot topic and challenge in research due to the difficulty in accurately quantifying it. Complementary models have gained widespread use for their ability to simulate evapotranspiration using only conventional meteorological data. While the key parameter \(\:{\alpha\:}_{e}\) has been demonstrated to vary with temporal scales and regions, the factors influencing this variability remain unclear, and dynamic parameterization methods are still lacking. This study conducted an analysis of the parameters and influencing factors of the complementary model (C2018 model) based on 14 eddy flux stations on the QTP, and fitted the relationships between parameters and environmental factors. The results showed that the calibration parameter values ( \(\:{\alpha\:}_{e}\) ) of the 14 eddy flux stations ranged from 1.07 to 1.54, exhibiting a strong correlation with the multi-year monthly average temperature and net radiation (correlation coefficients of -0.71and − 0.47, respectively). Using stepwise regression to fit the relationship between \(\:{\alpha\:}_{e}\) and environmental variables, and embedding these parameters into the C2018 model, approximately 86% of stations achieved a coefficient of determination (R²) and Nash efficiency score (NSE) above 0.75. This enhanced the model’s regional applicability and simulation accuracy. Compared to using a single parameter value, the NSE values for this study’s simulations were significantly higher across seven sites at the site scale, while RMSE and MAE are markedly reduced. This indicates that the deviation between the simulation results and observed measurements is smaller. At the regional scale, the model more accurately depict the spatial distribution of land surface evapotranspiration across the QTP, particularly in extremely arid regions (Qaidam Basin) and humid areas (southeastern QTP). The empirical formula for estimating \(\:{\alpha\:}_{e}\) proposed in this study provides scientific support for plateau evapotranspiration estimation, hydrological mechanism analysis, and water resource management.
