From Xian to Guangzhou, you can take Trains No.K84, K228, K646 and T266. Usually, the ticket is sold at the railway station three days ahead of your departure date. But if you buy the ticket from the ticket agencies, you should go to buy it ten days ahead of your departure date. For instance, if you want to leave Xian for Guangzhou on Feb. 17th, you should go to buy the ticket today. Recently, due to the Spring Festival, train ticket is very hard to buy. So, you'd better go to purchase it as soon as possible.