How far is it from Xi 'an to Vietnam? About how long does it take by plane?

It's far away, about two thousand kilometers.

The shortest way is to transfer from Guangzhou, which takes 8 hours.

You have to get a passport before you get a visa. Because there is no direct plane or train from Xi 'an to Vietnam, you can choose to fly to Guangzhou, which takes about 8 hours at the shortest.

If you take the train, I suggest you take the train to Nanning, Guangxi, and then take a bus to dongxing city, so that the border cities can leave Vietnam.