The Yuen Long Plain (Chinese: 元朗平原; pinyin: Yuanlang Pingyuan), in the northwestern corner of the New Territories, is the largest alluvial plain in Hong Kong. With an area of 144.3 square kilometres (55.7 sq mi), it was formed between the time of the Tang dynasty (618–907) and Song dynasty (960–1279). It covers Yuen Long Town, Tin Shui Wai, Lau Fau Shan, Ping Shan, Shap Pat Heung, Hung Shui Kui, San Tin, Lok Ma Chau, Pat Heung, Kam Tin, Nam Sang Wai, Mai Po, etc.
In the past it was mainly covered by marshes, fields and fish ponds. Yuen Long New Town and Tin Shui Wai New Town were built on the plain.