Using the NCAR/NCEP daily reanalysis data,the isentropic potential vorticity(ζIP) analysis of a heavy rain event from 9 June to 11 June, 2008 in North of Zhejiang was performed.It is found that the evolution of ζIP reflected the movement of heavy rain areas and development of SW jet.Heavy rain areas were mainly located in the southeastern part of high potential vorticity center,where the strong SW jet appeared.The precipitation in ζIP center was small,and it stopped when the center moved south. Through the vertical profile,it could be seen that the strong NW flow transported the high potential vorticity from high level to eastern low level. When north Zhejiang was under the control of positive ζIP advection, the heavy precipitation occurred.When it was under the negative ζIP advection control, the heavy precipitation stopped. In addition, formation of anti-Ferrel circulation near 30 °N provided favorable conditions for generation and maintenance of rainstorm.