Can I get a visa to go back to Shanghai?

I'm staying in China for a few months then, in august, I would like to go to Tibet and end my trip in Kathmandu. Can I get a new tourist visa over there to go back to China?
If so, how long can stay in China after that and am I sure not be stuck in Nepal with all y stuff in China? Is it easy to get it or may I experience some troubles?
Thx