China has a vast territory; urumqi is in the northwest while Sanya is the most southerly point of China. It will take about 65 to 77 hours to cover the distance by train providing there is no delay; besides, there is no direct train or bus between the two cities and you need several transfer. Thus you will be rather tired. You would better go by plane. Since there is no direct flight from Urumqi to Sanya, I suggest you fly to Guangzhou first and then there are many flights from Guangzhou to Sanya. This website provide a platform to booking flights and you can submit your reservation or write to them with your request.