Station to city center

The time is enough for you to catch the last subway, but you still need to take a taxi to your hotel when you get off. this website can do reservation for you in advance, contact them for help.

I know this is 6 years too late for the original question asker, but I note there was one concern that wasn't fully addressed in the original answer.

In my opinion, yes, it is perfectly safe to get a taxi or subway at any time in Xi'an, for people of all ages and genders. In general, most (but admittedly, not all) parts of China are an incredibly safe place to travel. Your only concern will likely be the danger of being overcharged for a taxi - known by locals as the Foreigner Tax or Foreigner price. Again, in my experience, the first price quoted is usually double the actual price - try offering half of what anyone suggests to you, then instantly walking away if they disagree. Often, you'll be called back immediately with a better price.