precipitation is a variable whose value, intensity, and type changes in temporal and spatial dimensions. the occurrence of heavy rainfall is an aspect of these changes which is a dangerous factor in the incidence of natural disasters such as flooding. In this study, with the aim of investigating the behavior of precipitation and discharge of Babol Roud watershed, the Talar station was selected as an indicator station. Then, the cycles governing precipitation and discharge parameters of the station were estimated at the annual scale (1976 - 2011) based on the spectral analysis technique. The results of spectral analysis on time series of discharge and precipitation at a 95% certainty level indicate the existence of a common annual 2 cycle in discharge and annual precipitation. The coincidence of a 2 years old significant cycle in the time series of precipitation and discharge means that in 2 years the repetition of annual precipitation events affects annual discharge. The Extraction heavy rainfall in the Babol Roud watershed was examined the study of atmospheric conduct at the sea level pressure (SLP) and the elevation of the atmosphere medium level (500 hpa level) at the time of their occurrence. After grouping these days, based on cluster analysis technique, three patterns were determined as the dominant patterns of heavy rainfall in the Babol Roud Watershed.