Rainfall ability for generated soil erosion is rainfall erosivity and unlike some other natural factors, such as relief or soil characteristics, is not amenable to human modification. It represent a natural constraint for land use and they management. Rainfall erosivity express in erosivity index which one of important and validate they is Wichmeier Smith (EI30 or R) erosivity index which used in universal soil loss equation or its revisit equation. Data limitation and defecault calculation of this index cause to extensive studies in relation to its modeling and preparation rain fall erosivity map in order to successfully evaluate potential erosion, preparation soil conservation plans and land management to be used. According to these items frist this index calculated in 5 avilable recording rain gauges station in Chaharmahal Bakhtiari province that its maximum and minimum whit amounts 1169.9 and 98.1(Mj.mm.ha-1.h-1.yr-1) Respectively obtained in Chelgerd and Brojen station. Then for analyze it in dimension time and Place and determination type erosivity rains this index whit rainfall erosivity density index calculate in time period monthly, seasonality and annual and through evaluated different interpolation method interpolated and average this amounts in region surface obtinated y using thiessen polygon method. Obtained results, mean erosivity and its density respectively 94.5and 0.71(Mj.mm.ha-1.h-1.yr-1-- Mj. ha-1.h-1) showed in region surface. Also maximum monthly erosivity and its density in region surface obtinated in Farvardin and Azar and for seasonal scale this factors respectilely shows maximum values in winter and spring.The obtinated resultes for interpolation this indexes in most time period showed highest amount in weast, northweast and southweast of the region. In order to determination equation for estimate erosivity index for regions lacking data from recording rain gauges, regression analysis in annual scale was used. Finally the best regression equation in form multiple linear and based on umber wet days(WD), annual 90th percentile(C90) and Institute of Agricultural Sciences of south Korea (IAS) was obtained. Then with use of this equation amount erosivity estimated in other station and whit use of actual and estimated value, rainfall erosivity map whit use of the most accurate interpolation method or ordinaly Co-kriging was prepared. The obtinated map shows complex pattern of erosivity in region which whit use of rain gauge station was reflected and generally shows maximum values around Chelgerd station in north weast and minimum values in east and northease region.