possibile to book the entrance buying the tickets online for Qinshihuang's Mausoleum Site Museum?

Well, the entrance ticket of this scenic spot is included in the Museum of Qin Terracotta Warriors and Horses.
As I know, the official website doesn't have English booking page. So it's ok to buy the ticket on th spot In usual time, there are always enough tickets for you to choose and there is no long queue.