whats the best way to get from changsha to Gansu?!

Gansu is a province. Which city in it you are heading for? Take its capital city Lanzhou for example, you can take a flight, which takes about 2.5 hours and ticket fare for tomorrow is about CNY 1,000 for an economy class seat. You can laso take a train, which takes about 21.5 hours at least; ticket fare is CNY 399 for a middle berth hard sleeper and CNY 629 for a middle berth soft sleeper.

thankyou!! we want to go to Dunhuang, to the Echoing sand mountain and the cresent oasis the trains didnt go direct so maybe flying would be best. can you recommend a good month to go?!

There is no direct flight between the two cities either and you can make a transfer at Lanzhou or Xian. May to September is good time to visit Dunhuang, when it is not cold and the scenery is beautiful. But I personally recommend you to avoid July and August, when is the summer holiday and the cost will be higher than usual.