If you want to go to Hainan island from Urumqi, anyway you should pass Guangzhou. To go to Guangzhou from Urumqi, you can change your train in many cities like Xi'an or Zhengzhou. I suggest that you go through Zhengzhou because there are more trains to Guangzhou than in Xian. The trip from Urumqi to Zhengzhou demande about 35 hours by fast train or 40 hours by ordinary train; from Zhengzhou to Guangzhou it takes 16 hours by faste train or 20 hours by ordinary train. After arrival in Guangzhou, you have to spend another 10 hours to go Haikou by train or by bus. Hope you have a good time in China!