The Meiyu season is a weather phenomenon that occurs in the middle and lower reaches of the Yangtze River in China, Taiwan, south-central Japan, and southern South Korea in June and July each year, and is called "Meiyu" because it is the ripening period of the plums in the south of the Yangtze River, and is known as the "Meiyu" season.

The rainy season in the air humidity, high temperatures, clothing and other easy to mold, so some people also called the plum rain with the same pronunciation of "moldy rain". After the rainy season, the weather begins to be dominated by the Pacific subtropical high pressure, officially entering the hot summer months.

The rainy season occurs mainly in the middle and lower reaches of the Yangtze River in China's subtropical monsoon climate zone, as well as in Taiwan, the Liaodong Peninsula, the southernmost part of the Korean Peninsula, and the south-central part of Japan. The rest of the world at the same latitude does not have the rainy season. There is no significant meiyu phenomenon in South China.

Every year, around late April to early May, cold air from the north and warm air from the south converge in South China, forming a quasi-stationary front in South China. About the second half of May, the warm air power to enhance the quasi-stationary front moved north to the Jianghuai region, into the Jianghuai quasi-stationary front (also known as the rain front). As the warm air from the south carries a large amount of water vapor, when it meets a colder air mass, it generates a lot of convective activity. Because of this period of time, the cold and warm air force is equivalent, so that the front stays in the Jianghuai area.