Recently heavy rainfall that occurs in last decade for Baghdad city is part of climate changes effect on Iraq in general and Baghdad in particular. Rain is considered the main part in the water cycle as it enters mainly within the water system and water balance; therefore present study put of a special criterion to determine the amount of rainfall and analyzed in order to quantify the amount and the diagnosis of heavy rain. The availability of data by Iraqi Metrological  Organization  and Seismology (IMOS) for time period (1985/1986-2014/2015) held achieve the research objective .There are many statistical methods figure out  the difference to determine the amount of rain, Climatology mean  (C M) is one of them specialized to separate the amount of normal rainfall from heavy rain. The climatology mean of rain for this study has been 15.2mm. Whereas in the rainy season exceeded this limit, in this case considered extreme season, while less than limit called normal rain. The results shown during 30 rainy seasons, have been 12 seasons exceed climatology mean, four of highest extremes rain have been happened in November. The highest extreme rain has been in 2014, with seasonal mean of 34.7mm. The monthly anomaly climatology mean (ACM) has been equal approximate 20mm, November 2014 was  equal this value , When calculating the total amount of rainfall for the city of Baghdad during the 30 rainy season found that lightest mount fall  676 mm in January followed by the lowest rate month of November 596 mm, while the lowest amounts of rain fell in October and September, which did not exceed 130 mm.