For China, Tibet is one of his 5 autonomous regions, where they have their own government and so on. In reality, it's totally different. Some students we met here in JNU, told us that Tibetans are not welcoming with chinese people, they don't speak chinese they have their own alphabet, and they were shocked when we told them that we wanted to go there.
That not surprising, China and Tibet have a long common history of disagreement and fight.
In 1949, when Mao proclaim people's republic of China, he also affirm the control of Tibet by China with his military power. Since then, 1965 is the year where Tibet is declare by chinese as the autonomous region of Tibet.
Nowadays China, where press is not free, forbid the word "Tibetains revolution" or "tibetans events", for its people to think on the government way instead of the tibetans way.
For Beijing, Tibet represent a strategic issue on many points: economic, territorial, and geopolitic.
Tibet abounds of mineral resources, water and biomass forest that represent a lot to Beijing. Grand Tibet represent more than 1/4 of chinese territory and occupy one strategic position because its the gate between eastern and middle eastern. Moreover, it has about 3000 km of common frontiers with Myanmar, Pakistan, India… More countries that China considers like economic and geopolitics enemies.
Sources: http://www.lemonde.fr/asie-pacifique/article/2008/03/23/chine-et-tibet-une-si-longue-histoire_1026383_3216.html
http://www.lemonde.fr/asie-pacifique/article/2008/03/26/crise-du-tibet-des-enjeux-cruciaux-pour-pekin_1027497_3216.html