Miyun County, located in the northeast of Beijing, is a key drinking water source and ecological conservation area of the Capital. Miyun is the junction area between Yanshan Mountain and North China Plain. It is the key entrance from North China to Northeast China and Inner Mongolia and is known as “Key of the Capital”. The county is surrounded by rolling mountains on three sides, i.e. east, north and west, with the magnificent ancient great wall winding through the high cliffs and valleys. It also holds the wavy Miyun Reservoir in the center and diluvia alluvial plain in the southwest. The topography is shaped like a fan with mountains by three sides, lowland in the center and opening on the southwest.
Miyun County stretches from E 116°39 ′33" to E 117°30 ′25 ", with a length of 69km from east to west, and from N 40°13 ′ 7" to 40°47 ′57", with a width of 64km from south to north. It borders on three counties of Chengde, Hebei, i.e. Xinglong, Chengde and Luanping, to the south and north, and Huairou District, Shunyi District and Pinggu District to the west and South.