You can take 611 from the train station to Duan Cu Men station (via: 5 intersection, Min Leyuan, Dachai chai city, Duan Cu Men), and get off the bus and walk across the street to Lao Sun's place. Ticket is 1 yuan, and it will take you about 20 minutes (without traffic), or in case of traffic it will be about 30 minutes. It's a busy street in downtown Xi'an, so there's a lot of traffic, so you have to think about it, and it's better to have plenty of time.
Prices have risen, and Sun's original price was 15 yuan, now estimated at about 25 yuan, but if you are passing through Xi'an, I suggest that you do not taste it, because it is all hand-breaded buns, not broken buns, so you simply can not time
If you really want to eat, I will give you the location, but also authentic, is the train station, west of the intersection of the 7th Road, there is a Guanghua hotel diagonally across the street
If you really want to eat, I give you a place, but also authentic is the train station, west of the 7th Road, there is a Guanghua hotel diagonal opposite the hotel.
It's called Old Ma's Bun Restaurant, and it's also very authentic and has a long history. I'm sure you're just passing through Xi'an and don't have a lot of time to spare
You can take a bus to Dongwu Road. Old Sun family mutton steamed buns (Revolutionary Park diagonally across the street), you can eat there, by the way there are bags at the door. There are bags that cost more than 5 bucks, or 10 or so. It doesn't take long to get there, just 10 or so minutes.
If you want to walk, you can also, from the train station that city gate out. Go straight, see the first intersection and walk west, you can see it
Xi'an's train station near there is no authentic steamed buns. If you really want to eat good flavorful steamed buns you have to go to one of those smaller stores. I think places like Sun's are just famous, I've eaten there and it's not good, not even as good as the one in front of my house. Suggestions or find some small stores, the brand is not necessarily very loud, the location is not necessarily very busy, but as long as you choose the right place, you will not regret it, but there are too many of these places, but also very good to find, YOU can try to find them out!!!!