This study forecasts rainfall amount with the use of time series approach in Kabodar Ahang district which located in north part of Hamadan province. Seasonal model results revealed that precipitation data in mentioned district has non-periodic characteristic. Also, HEGY test results show no root in monthly and seasonal data. So, ARMA (4.4), can forecasts and exhibits mentioned region’s rainfall pattern mannerly.. By determining rainfall amount and applying underground water balance of Kabodar Ahang, accessible water of agriculture sector estimated for 2008 though 2010 equal to 257.77 , 267.56 and 254.87 .