Abstract: Basically, the low level moist condition is regarded as one of the most important prerequisites to heavy-rain forecast, so it is very often to ignore the upper level moist condition, which is depicted clearly on satellite water vapor imagery. Although many studies have declared some relationship between the heavy rain fall and the water vapor plume (WVP), however how and why the upper level moist condition contributes to heavy rainfall are still unclear.The relationship between the tropical water vapor plume and heavy rainfall durin g 20-25 July, 2002 was analyzed using GMS-5 infrared black body temperature (TB B) data as well as NCEP/NCAR 1°×1° reanalysis data. Results demonstrate a close relationship between WVP and heavy rainfall as follows. In the storm period,（1）a remarkable tropical WVP stretches northeastward from the Bay of Bengal to the Korea Peninsula, and moisture clusters were found surgi ng one after another from lower to higher latitudes in the WVP. The moist-surges were not only depicted as the horizontal advection in the middle and upper levels but also meant the whole levels' moisture transportation in the moist channel, since each time the low level jet (LLJ) was found accompanying to the southea st of the moist-surge when it burst northeastward, and the wind core also moves with the moist surge.（2）the north edge of the WVP was almost parallel to the upper level jet (ULJ) axis, and the meso-scale convective clusters (MCS) develo ped in the right back side of the southwesterly ULJ, within 3 latitudes away from the ULJ axis. The existing ULJ provided well outflows of air in the upper levels (divergence mechanism) which obviously benefit to MCS evolution.（3）A high θse tongue (θse≥350 K) maintains within and in parallel t o the direction of the WVP during the heavy rain period. The low level θse tongue indicated the area of high energy accumulation, above and around w hich was the most possible unstable area, therefore the heavy rainfall easily occurs. （4）Similar to theθse distribution in the WVP, a narrow and strong 850 hPa positive vorticity belt stayed in the WVP, which indicated the lifting m echanism in the low levels, and the cores of the positive vorticity correspond to MCS development.