Moisture transfer around the low level jet (LLJ) and its effecton rainstorms are studied. based on thc data of the Heavy Rainfall Experiment over South China during the "early flood"seasons of 1977 to 1979. It is found that development of rainstorms associated with the LLJ is caused mainly by lateral convergence of moisture under the LLJ axis rather than at the same level with the axis. The flow of moisture under the LLJ moves from right to left, as-cends in the storm area, turns right at higher levels above theaxis and then subsides. Thus a meso-scale cell of moisture trans-portation is formed, which is superimposed on the large scalecirculation around the LLJ, a feature favorable for the main-tenance of rainstorms. Winds in the boundary layer under the LLJ veer with altitudedue to friction. This accounts for the lateral transfer of moisture.Hence rainstorms may develop anywhere on the left of the LLJ.