Introduction:The Airport Express links central Beijing to Terminal 3 within just 16 minutes, and Terminal 2 from Dongzhimen, central Beijing is no more than 25 minutes away. The distance between Dongzhimen and Beijing Airport is 23 km by car. It presently costs RMB 16 for airport express There are 4 stops along the express rail link: Terminal 3, Terminal 2, Sanyuanqiao  and Dongzhimen. Dongzhimen will be the final city terminus. The Infrastructure Powers That Be, fully recognizing the current transport mélange at Dongzhimen, are putting the touching pieces to the Dongzhimen Transport Hub. The Airport Express will come into the hub on Basement Level 4, with Lines 2 and 13 a few floors above. You’ll actually be able to follow the signs and complete the interchange without ever seeing a ray of light (sun or moon). After the Games, you’ll even be able to check in your bags from Dongzhimen.

The line will have only four stops along the entire line. There will be two stops in central Beijing — Dongzhimen and Sanyuanqiao — with the two remaining stops at Beijing Capital International Airport. The Airport Express reaches Terminal 3 before reaching Terminal 2; passengers for Terminal 1 need to use the transfer passageway at Terminal 2.
Service intervals are expected to be 5 minutes at the start, with the entire trip taking around 18 minutes (Terminal 3) or 25 minutes (Terminal 2).
The new subway line will be a driverless system.

Terminal 3 station is covered by a cavernous steel archway
Passengers can check flight information immediately upon exiting the train. Passengers arrive through the northeast entrance to a transfer center comprising four passages. One passage in the middle reaches Terminal 3; two on the side lead to departure hall of Terminal 3 and the last passage in the middle connects to the arrival hall. All passages are navigable within a five-minute walk.
One minute after stopping at this station, the train will progress towards the Terminal 2 station.
After stopping at Terminal 3, the train progresses back in the opposite direction before making a huge turn on its approach to Terminal 2. The short journey takes approximately three to four minutes.

Timetable:
The first train departs from Dongzhimen Station at 6:00.
The last train departs from Dongzhimen Station at 22:30.

The first train departs from Terminal 3 at 6:21.
The last train departs from Terminal 3 at 22:51.

The first train departs from Terminal 2 at 6:35.
The last train departs from Terminal 2 at 23:10.

Airport-bound trains depart from Dongzhimen from 6:00am-10:30pm. City-bound trains depart Terminal 3 from 6:21am to 10:51pm and Terminal 2 from 6:35am to 11:10pm.

Route
The Airport Express runs in the following sequence: Dongzhimen → Sanyuanqiao → Terminal 3 → Terminal 2 → Sanyuanqiao → Dongzhimen. Riders can transfer to Lines 2 and 13 at Dongzhimen and to Line10 at Sanyuanqiao.
Most of the 28.1 km of tracks are on the surface, except for a 4-km segment between Dongzhimen and Sanyuanqiao, several minor crossings underneath existing railways lines, and the terminal connection within the airport.
Please note that there is only T3 to T2 train and there is no reserve direction trains. The T3, T2 and Sanyuanqiao is just like a big circle - the train only goes counter-clockwise.

The Price:
25 RMB (or 3 USD) for a single trip. No matter which train station you get off.

Photos:

Waiting room:

Beijing airport express:

Inside:

Outside:

Platform:

Tickets/information desk: