The symposium will take place at the College of Chemistry and Molecular Engineering, Peking University (PKU). The auditorium is at Room A204 for the first day (Aug 4), and is moved to Room A717 for the second and third days (Aug 5-Aug 6). Both the two rooms are in the region A of the chemistry building. It is relatively easy to find a building called Founder near the subway station 'East Gate of Peking University', and the chemistry building is right behind it.
Region C of the chemistry building, view from north gate
Region A of the chemistry building, view from south gate
In case that you will need to go to the auditorium by taxi, here is the Chinese address card (its png version).