In this paper, in order to study of the highest daily precipitations of daily precipitations data in 46 synoptic and climatologic stations that almost covered all part of Iran have been got from the national weather organization and have been used after the extraction of necessary data for a 30-year period from 1976 to 2005. In concerning of data analysis, necessary statistical analyses like data homogeneity test, normality test, correlation test, simple and multiple regressions, variance analysis, Friedman's non parametric test and classification cluster analysis have been used. The results showed that the average of the highest precipitations in all the studied stations during the statistical period of the research, except in two stations of Boushahr and Khoy, don't have any significant difference. Investigation of the changes of the highest annual precipitations in the statistical period in each of these stations showed that these changes are significant in Sanandaj station and in the other stations no significant change is observed. The results also proved that there is a positive and significant relation between the highest daily precipitation and annual precipitation in all the stations which means increase in the annual precipitation the highest daily precipitation of stations growth. Finally climatic classification of the stations displays 5 layers in terms of the proportion from highest daily rain to annual rain in the country.