Dragon Boat Races are a traditional part of the Chinese festival called 端午节 [duān wǔ jié]. It is celebrated on the 5th day of the 5th month in the lunar calendar. This year (2018), it falls on Monday June 18th. This festival commemorates Qu Yuan (340-278 BC), an ancient Chinese official and a poet, who drowned himself rather than serve a new king during the Warring States period of Chinese history.
In addition to the races, Chinese people celebrate the festival by eating zongzi 粽子 [Zòngzi], and drinking realgar wine 雄黄酒 [xióng huáng jiǔ]. Zongzi is a rice dumpling wrapped in a bamboo leaf and boiled with a tasty morsel inside. There are lots of regional variations. Realgar wine is an alcoholic drink with some insecticides added. This is actually poisonous but, in the past, was used to drive away evil spirits.
You can learn more by following this link: travelchinaguide