First you will need to have your Campus Card ready (xiaoyuanka 校园卡). You will have to get the card registered for PKU library use.
When you first get into the PKU library (from the South entrance) you cannot yet use the card to get through the scanner gates. Tell the guards that you want to get the card registered (zhuce 注册). Now you have to get to the Card and info booth just right from the entrance to the main hall.
For each month of usage you will be charged RMB 10 (max. RMB 60 for the whole semester). You can have the card registered for a shorter time but can’t make extensions later.
If you want to lend out books, you will be have to pay a deposit of RMB 1000. Make sure to keep the receipt since you need it when you want to get the deposit back at the end of the term.