Subway planning had determined that Beijing West railway station would be the interchange between Lines 7 and 9.

On December 31, 2011 the 11.1 km (6.9 mi), nine-station southern section from Guogongzhuang to Beijing West railway station opened.

[11] Passengers had to transfer to shuttle buses that connected to the main subway network to continue their journey.,[12] making the line sparsely used in 2011.

[14] The extension would terminate at Xi'erqi station and help relieve the congestion on the western arc of Line 13 and more directly serve Tsinghua University.

On December 30, 2012, the original northern section from the Beijing West railway station to the National Library entered into operation.

[17] Line 9's passenger traffic began to grow rapidly after the northern section went into operation.

As of January 2013, the average daily passenger traffic was already three times higher than in December 2012,[18] at 220,000 rides.

[20] However, in reality during construction, only the south extension project of the Changping Line from Xi'erqi to Jimenqiao Stations actually started construction, the last remaining section of the Changping Line’s south extension to Mingguangqiao West Station and the entire northern extension section of Line 9 (Mingguangqiao West to National Library Station) was put on hold.