Sanhe City, a county directly under the jurisdiction of the finance of Hebei Province, and a county under the jurisdiction of Hebei Province, is managed by Langfang City. It is only a river away from Beijing, and it is a county-level enclave with the largest area and the highest administrative level in China. It is located in the north northeast of Hebei Province and the northernmost of Langfang City. It borders Jizhou District of Tianjin in the east, Pinggu District of Beijing in the north, Shunyi District of Beijing in the northwest, Tongzhou District of Beijing across Chaobai River in the west, Dachang Hui Autonomous County in the southwest, Xianghe County in the south, Baodi District of Tianjin in the southeast, with a total area of 634 square kilometers. In 2021, the registered residence population of Sanhe City will be 768800. As of August 2022, Sanhe City has 6 streets and 10 towns under its jurisdiction, and the municipal government is located at No. 5, Dingsheng East Street.

During the reign of Emperor Kangxi in the Qing Dynasty, the imperial palace was built in Yanjiao, Sanhe, which is reputed as "the palace under the feet of the Emperor". According to the "Unified Annals of the Qing Dynasty", "it is named for its proximity to the water of Li, Ru and Baoqiu." In the second year of Wude in the Tang Dynasty (619), it was analyzed that the eastern part of Lu County in Xuanzhou was located in Linlu County. In 1993, Sanhe County was abolished and Sanhe City was established.

In 2021, Sanhe's GDP will be 59.52 billion yuan, an increase of 8.3% at comparable prices. Among them, the added value of the primary industry was 1.93 billion yuan, up 6.9%; The added value of the secondary industry was 16.6 billion yuan, up 2.9%; The added value of the tertiary industry was 40.99 billion yuan, up 10.5%. The ratio of the three industrial structures is 3.2:27.9:68.9.