Reference evapotranspiration (ETo) is one of the most important components of the hydrological cycle, whose correct estimation is very important in the design and management of irrigation systems, environmental studies and water resources. In order to conduct climate research, the use of network data and the output of climate models requires evaluation and validation. Therefore, the current study was compiled with the aim of evaluating the accuracy of the latest CMIP6 models in estimating reference evapotranspiration in Iran. For this purpose, the historical data related to 10 CMIP6 models were extracted from the USGS database and the amount of ETo was estimated in 44 synoptic stations of Iran for the base period and the historical period of the models (1985-2014) using the Hargreaves Samani method. MSE, RMSE, MAE, MBE and Taylor's diagram were used to verify the accuracy of the models and the corresponding observed values. The results of evaluating the accuracy of the models in monthly, seasonal and annual scales showed that. BCC-CSM2-MR and MRI-ESM2-0 models have higher accuracy for estimating evaporation-transpiration compared to other models in Iran region, and MIROC6 model with RMSE value (1.91) has the weakest performance among them. The studied models have shown. Regionally, in general, the error of the BCC-CSM2-MR model is higher in the northern and southern regions of the country than the MRI-ESM2-0 model. Also, the MRI-ESM2-0 model shows more error than the BCC-CSM2-MR model for the highlands of Zagros. The error rate of these models in arid zones of Iran,