Drought, is natural phenomenon that damage to natural ecosystems and human life and, As a climatic anomaly, is considered one of the most destructive weather phenomena that occur in almost all climatic regimes. Drought this natural phenomenon, harmful and costly consequences which affects the area of ??influence. The position of the belt of arid and semiarid regions of the world, no country is immune from this phenomenon and And the effects of this damaging experience to its normal position. Severe droughts and extensive damage may occur in many parts of the country to impose economic bodies every year, Therefore , one of the basic needs and characteristics of drought events in the study of environmental and water resources planning. In recent decades, many of the drought on the stream flow drought index As a hydrological drought forecasting and assessment methods of researchers has been. We are constantly faced with problems in The analysis of the index during the period in areas with little or no statistical areas . To alleviate these problems used analysis frequncy method. Because of the nature of regional droughts occur And usually cover a wide area and persist for a long period of time, It is important to study the concept of regional. In this study to evaluate and predict the hydrological drought in the Drodzan dam watershed,used regional frequency analysis based on stream flow drought index. The end result of the drought in the study area to assess the results of the standardized precipitation index (SPI) were compared. During the first nine stations had adequate data for the study were selected. After rebuilding the SDI index data flaws on time scales of 3, 6, 9 and 12 months during the period (1986-2011) were selected stations. After drought conditions, according to the SDI index, Examined regional homogeneity of homogeneity index based on line-moment method . The results showed that region can be considered as a homogeneous hydrologic region. The Goodness of fit test chi - square and Klomoronov - Smirnov normal distribution for the index of stream flow 3 monthly distribution values ??are somewhat generalized to indicators of stream flow, 9 and 6 months, and exponential distribution for indicators of stream flow at 12 months, they were known as the best distribution. Thus, SDI index related to the time scales specified return periods of 2, 5, 10, 20, 25, 50, 100, 200 years was estimated at each station. The regional analysis was performed using multivariate linear regression and presented The models. The return period associated with any of the conditions of drought in any of the periods of 3, 6, 9 and 12 months from the curve analysis of each station to obtain and use the software Arc GIS mapping zonation of them drawn. The results of the Zoning Maps shows that Among the areas that are experiencing severe drought in the north and north-east of the range, compared to other regions may experience more severe droughts, and With increasing return period drought covers almost the entire region The SPI drought index has been calculated and the results were compared with the results of the index SDI. Although the results of SDI indicator shows more sensitivity to drought, but the results were similar indexes of drought shows in recent years had greatly increased. Therefore, these areas are subject to damage and economic damage - Hydrologic drought is social and therefore more attention is needed on water resources. Keywords : drought, hydrological drought, stream flow drought index (SDI), standardized precipitation index (SPI), regional frequency analysis, zoning