Dignosis shows that the basic contributing factors caused the exceedingly heavy rain during August 4-5, 1993 in southern Shandong Province are as the following. Under the suitable circulation background as subtropical high intensified and spreaded westward,and the plateau trough moved eastwards with the southwest vortex,warm and wet air with southerly jet at the low layer were transported and reached over the stationary front (from west to east) in the front of the convergence core of the law vortex,and forced lifted, then, MCC (Meso-scale Convective Complex) generated, devdoped, and regenerated.