Abstarct: One of the biggest problems and challenges of men in 21st century is climate change. In this regard, climate scenarios should be developed to forecast climate situations in future. Yet the most important tools for developing such scenarios are Atmosphere-Ocean General Circulation Model (AOGCM). Due to the importance of these versatile models, the choice of the best model for studied regions is of great concern. Therefore in this research, four GCM models as BCM2, CNRMCM3, MIROC3.2 and HadCM3 are chosen among the climate models. Selection criterion of the first three models is network similarity and as for HadCM3 model are dimensional analogy with the three models and excessive usage in climate researches. Performance test and verification of these models for data simulation of three parameters: precipitation, maximum and minimum temperature in six regions as north-east, north, north-west, center, south-east and south-west of Iran in the past (1981-1999) are investigated using performance factors R2, RMSE and Nash-Sutcliffe coefficient. Then for each region, the optimized model is selected and for these three aforementioned parameters, the effect of climate change on precipitation, maximum and minimum temperature for each region of country is studied according to the selected model using proportional downscaling method with emission scenarios A2, A1B and B1 in future era (2046-2065). Results show that maximum precipitation amount in future in most regions among first three scenarios occurs at the end of winter and beginning spring with A2 scenario and minimum precipitation amount occurs in most regions in summer with A2 and A1B scenarios. Maximum and minimum temperature of all regions with these three scenarios increase as well.