What is the best way to travel from Beijing to Xian? Is it possible to do the trip in one day?

The fastest way is by air, about two hours. Or you can take the bullet trains from the Beijing West Railway Station, you can reach XA North in four or five hours, which is much cheaper. In both ways, you can get to the destination in one day.

If you want to spend a whole day in XA, the best method is to take an overnight train. You can leave Beijing in evening and reach XA early next morning, which will not effect yout trip. After that you can fly back to Beijing.