how can i go to whenzou from guanghzou and what will cost cheap by train or by air? how many time it

There is only one train between the two cites and it is K326/K327. The ticket price is around 337 to 361RMB for hard sleeper. The trains take about 22 hours and 45 minutes.
It is hard to tell you the flights' tickets price, because if you book the tickets early, you may get a large discount. The plane takes about 45 minutes.