Abstract: The relationship between the south-west monsoon tide (SWMT) and the precipitation from April to June in China is analyzed in terms of the examples of two rain storms in South China on 8 and 11—21 May 2004. The preliminary result shows that the outbreak of the SWMT is connected with the cross-equator flow (CEF) coming from the south hemisphere immediately. By means of the weather map, grid wind data, satellite cloud images as well as the Quikscat wind fields at 10 m level over sea surface, evidence shows that the main northern precipitation influencing systems including cold front, occluded front, ground small high pressure, upper troposphere cold vortex, inclined trough, shear line and so on. The cold air guided by these systems moves southward and plays an important role in the formation of the heavy rainfall. The southern precipitation systems are the water vapor and the cloud band caused by the outbreak of the SWMT leaded by the CEF at 85°~95°E (the longitude degree of the bay of Bengal) and 105°E, and the tropical cloud cluster is formed by the interaction between the SWMT and Himalaya Mountains. These cloud clusters with high temperatures, high humidities and high instabilities are transferred to the south and southwest of China and interact with the cold air, cause the rain storms and persistent precipitations. The analysis shows that the precipitation systems are closely connected with the "large-scale system between the two hemispheres". They are the primary cause of strong convective weather, rain storms and tornados generated over southern China.The precipitation progresses is mainly connected with SWMT over the bay of Bengal region. But the South China Sea monsoon tide hasn't occurred at that time. So the South China Sea monsoon tide can be regarded as one part of the Asia south-west monsoon tide. In order to get the final conclusion, more studies on this question should be done in the future.