Abstract   Synoptic climatology studies the relationships between the atmosphere circulation and the surface environment of a region. This study was done during low precipitation years in Iran(۱۹۸۳, ۱۹۸۵, ۱۹۸۷, ۱۹۸۹, ۱۹۹۰, and ۱۹۹۹). In order to explore the spatial and temporal variation of ۵۰۰hpa flow patterns and their relationship with the precipitation of Iran , daily geopotential heights for the region ۰º E to ۷۰ º E and ۱۰ º N to ۶۰ º N ,at ۲.۵ degree resolution, were analysis. A PCA analysis of geopotential heights in S-mode showed that there are seven significant map patterns. These are explaining about ۹۳ percent of variance. The ۱st of map patterns(MP۱) represents latitude flow and ۲,۴,۵,۶ and ۷ patterns determine ridge over Iran. Flow patterns lead air masses toward Iran which the causes low precipitation of the country.