Dachengzi is a town in Miyun District, Beijing, China. It lies within a valley, and the Hongmenchuan and Qingshui rivers flow through it. The town's population was 9,443 as of 2020.
Dachengzi is bordered by Taishitun and Beizhuang Towns to the north, Shangshidong Township and Liudaohe Town to the east, Zhenluoying and Dahushan Towns to the south, and Jugezhuang Town to the west.