By employing the NCEP/NCAR reanalysis data, the FY2C satellite water vapor images and the conventional meteorological data, in combination with the digitized satellite water vapor imagery and atmospheric dynamic field, the characteristics of dry intrusion and evolution and its impacts on the heavy rain during 17-18 July 2009 in Shandong Province are diagnosed. The results show that the upperlevel trough and lowlevel wind shear cyclone were helpful to the heavy rain process. There existed a strong relationship between the evolution of the dry instruction and the heavy rain process, and the dry intrusion originated from the midhigh level tilted eastward with height; heavy rainfall occurred at the forefront of the dry intrusion on the wet side of the zone where humidity gradient was at its maximum. The dark zone at the satellite water vapor image had a better correspondence with the dynamic field corresponding with the distribution of the high potential vorticity, high potential vorticity, and low humidity at 350 hPa, and the downward cold air characterized with high potential vorticity and low humidity in the upper troposphere enhanced the development of the lowlevel cyclone. The dry cold air intrusion contributed to the formation and maintenance of the dry layer, which enhanced the convective instability during the development of the heavy rain process.