Based on the conventional observation，automatic weather station precipitation，satellite cloud images and radar data, the heavy rain occurred between 9 and 10 2009 in Shandong is analyzed． The results reveal that the heavy rain attributed mainly to a lowlevel cold shear line. The heavy rainfall mainly appeared on the right side of the lowlevel cold shear line，the northeast quadrant of the southwest vortex, and the left front of the lowlevel jet, i.e., the coupling areas of lower and upperlevel jets. The southwest jet, located on the west side of the subtropical high, established the water vapor channel from the South China Sea to the central North China， which provided adequate warm, moist air and energy for the development of heavy rain, the necessary condition for the longtime stagnation of the lowlevel shear line. At the same time, the southwest warm and wet jet strengthened the convergence of the vortex by injecting water vapor and energy into the vortex of the shear line．The ground frontal cyclone was the trigger of the heavy rain. The convergence of the northeast cold air and the southwest warm and wet air over Shandong enhanced the convection and release of instability energy produced by the rainstorm． Under the condition of lowlevel convergence and highlevel weak divergence, the vortex motion in the vortex region strengthened the motion of the water vapor parcel. When some mesoscale convective systems (MCS) passed through the heavy rain area，the radar echoes showed mixing echo zones composed of stratiform clouds， which means that the convection was not strong．