In this research, impacts of climate change on the streamflow hydrological status of the Arazkooseh River are discussed. After Calibration and validation of the LARS-WG, HadCM3 was downscaled under A2 Scenario in three climatology station. Beside, calibration and validation of the SWAT model were done by observed data relative to past period of times. Streamflow values are then predicted using climatic parameters of period of 2011-2030, 2046-2065 and 2080-2099 years via SWAT model. The results indicated that the average annual temperature will increased around 0.8, 1.2 and 4.9 °C in desired periods, respectively. Precipitation values will increased 8.8 and 11.2 percent in the early and mid- century and it will decreased with 7.8 percent in the last years of century, correspondingly. The peak of rainfall will moved from month of March to the December. Because of climate changes, streamflow will increase 13 and 5 percent in the near periods. By contrast, in this case, it will reduce around 18 percent in far future. In this case research, the river discharge will increased in autumn and will decreased in spring seasons. Likewise, results of estimation showed that the annual peak flow will shifted from month of March to the April.