The Daxing Line of the Beijing Subway is a rapid transit line that connects the southern Daxing District of the city with the subway network. It extends Line 4 south from its southern terminus at Gongyixiqiao, on the 4th Ring Road in Fengtai District, to Tian'gongyuan, beyond the 6th Ring Road in Daxing District. The Daxing Line is about 21.76 km (13.52 mi) in length with 18 km (11 mi) underground. Daxing line contains 12 stations and is about 21.76 km (13.52 mi). Initially, the Daxing line was planned to have 4 ground stations. However, due to lack of space, only Xihongmen was built above the surface. Full-scale construction began in 2007 and the line was opened on 30 December 2010, 14:00 local time. Daxing line's color is teal, the same as Line 4.

The Beijing Subway is the rapid transit system of Beijing Municipality that consists of 27 lines including 22 rapid transit lines, two airport rail links, one maglev line and 2 light rail lines, and 490 stations. The rail network extends 836 km (519 mi) across 12 urban and suburban districts of Beijing and into one district of Langfang in neighboring Hebei province. With 3.8484 billion trips delivered in 2018, an average of 10.544 million trips per day, the Beijing Subway is the world's busiest metro system. Single-day ridership set a record of 13.7538 million on July 12, 2019. Being 836 kilometres (519 mi) in system length, the Beijing Subway is the longest metro system by route length, surpassing the Shanghai Metro in December 2023.