Sihai is a town in the Yanqing District of Beijing, China. It is located in the northern part of the municipality, within Yanqing's mountainous terrain.
The town borders Qianjiadian Town and Zhenzhuquan Township to the north, Liulimiao and Yanqi Towns to the east, Bohai and Jiuduhe Towns to the south, and Yongning Town and Liubinbao Township to the west. As of 2020, Sihai had a population of 4,434.