In this research, from data of 26 hydrometric station records and l-moment approach, regional and stational flood frequency of Dez basin was analyzed. For identifying homogeneous regions, Ward hierarchical cluster method was used. The appropriate number of homogeneous regions was determinate from nonhomogeneity test and discordancy measure. The Dez Basin was divided into three homogeneous regions. In these regions parameters of the regional frequency distribution were evaluated by the L-moment ratios. The L-moment diagram, goodness of fit test, and plotting position methods were used for the selection of appropriate distribution and plotting position formula. Generalized Extreme-Value distribution and Chegodieve plotting position formula is appropriate for region A, generalized logistic distribution and Greengurten plotting position formula for region B and Generalized Extreme-Value distribution and Greengurten plotting position formula for region C were selected. The relative root mean square error (rRMSE) between observed and estimated data, in all stations, in high return periods is small and in small return periods is vicversa. Regional models evaluated for determination of flood discharge magnitude in different frequency by linear and multiple regression method
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