The advance and retreat of summer monsoon affects the transition of the rain belt in the eastern part of mainland my country. From April every year, the rain belt moves from south to north, and then retreats from north to South after September. Therefore, the rainy season in South China is earlier and longer than that in North China. The "disorder" of the advance and retreat of summer monsoon and rain belt often leads to drought and flood disaster. If the advance is slow and wandering in the south for a long time, it will lead to "waterlogging in the South and drought in the north"; If it advances rapidly and stays in the north for a long time, the situation of "waterlogging in the north and drought in the South" will occur easily.