Im traveling to Baiyin in late August. How far is it to Tibet?

You must refer to Baiyin city of Gansu province, right? Well, I heard it is around 1,800km between the two places.

No direct train operates from Baiyin to Lhasa (the capital city of T). I suggest you take a bus from Baiyin to Lanzhou first. There you can catch a train to your destination, but the train duration is a little longer than 26 hours.