This research aims to study the distribution of Phytoplankton in four locations which have different environmental specifications, in addition to study some environmental factors of Alhaffeh Dam water that affect the distribution of the phytoplankton (Temperature ,BOD, DO, pH, NO3, NO2, NH4, PO4). Samples were collected from different locations of the Dam basin from June 2011 to May 2012 once or twice a month. (84) species of Phytoplankton were identified and were distributed as: (38) species of Chrysophyta, (36) species of Diatomophyceae, (2) species of Chrysophycea, (25) species of Chlorophyta, (20) species of Cyanophyta, (2) species of Pyrrhophyta, and (5) species of Euglenophyta. The results show apparent changes in physical and chemical properties of water during this study. This is the first study of the phytoplankton on the water of Alhaffeh Dam.