Take subway line 4. According to Baidu map, Xiyuan Hospital needs to take Metro Line 4 to Guang 'anmen South Street, which takes 35 minutes. The specific bus routes are as follows:

1. First, walk about 570.0 meters from Xiyuan Hospital to Xiyuan Station subway station, take Daxing Line of Metro Line 4 and pass 7 stops.

2. Next, get off at the National Library Station, change to Metro Line 9 in the station, take Metro Line 9, pass four stops and get off at Beijing West Railway Station.

3. Finally, walk about 75.0 meters to the South Square of Beijing West Railway Station, take bus No.410, pass four stops and get off at Guang 'anmen South. Walk about 305.0 meters to the end of Guang 'anmen South Street.