Based on meteorological monitoring data in Guangdong Province, the Shanwei radar data and global reanalysis data CFSR, this study analyzed the processes of two record-breaking extremely severe precipitation events in August 2013 and August 2018 over the eastern part of Guangdong, aiming to expound the effect of boundary layer jet. The results are as follows. (1) The main influence systems of the two processes respectively were the long time slowly-moving residual circulation of Typhoon Utor and the outer circulation of monsoon depression. When the eastern region of Guangdong was located on the southeast side of typhoon circulation or the east side of monsoon depression, the convergence and uplift of boundary layer jet formed clear mesoscale energy fronts, which were the favorable conditions for severe precipita-tion. (2) Boundary layer jet provided abundant and continuous water vapor conditions for the severe rainfall, cooperated with the effect of special topographic friction and countercheck, thus remarkable convergence of water vapor flux was formed in the east of Guangdong. (3) During the development of persistent heavy rainfall, the atmospheric stratification was unstable for a long time, which was closely related to the continuous transport of warm and wet advection in the lower troposphere. The major differences between the two processes mainly lies in the differences of intensity and wind direction of boundary lay jet, thus the way of airflow convergence and scope of severe rainfall were significantly different.The role of boundary layer jet is revealed more significantly during the influence process of monsoon depression.