Heat wave has harmful effect on environment and human life. First of all, this research identifies the heat wave of four provinces of Ilam, Kermanshah, Lorestan, and Khuzestan, for the period between 2000 and 2010. This study uses the heat index, and the return period of this wave using the Gambel distribution function. According to obtained results, total redundancy of extracted heat waves was detected as 143, which 70 waves of this amount have been in warm period and 73 waves in cold period of the years. Monthly process of thermal waves shows that the highest wave was occurred in the month of Farvardin. Process the maps of surface pressure of the earth during warm period of the year shows that low pressure tabs of Ganges had pulled near the central Iran, even its tabs in to north east of Iran and the center of Iran is low-pressure heat. In time of occurrence of this wave, there was pressure heat occurred in the earth surface from Horn of Africa, Europe, Iraq, and Saudi Arabia. Hence, the low pressure tab of Saudi Arabia has been affected southern, south-western, and western parts of Iran. Synoptic Process of the heat wave condition shows that area is located in front of the hot air and the influence of hot air on the area has caused the temperature rise at this time of the year.