I don't think that's really China's view.
The Wikileaks cables have included suggestions that Bejing is willing to accept a unified Korea under the South's government
China is also seriously concerned about an influx of refugees should North Korea 'collapse'.
And that's really everybody's concern. North Korea can't be allowed to simply 'collapse'. (It really already has collapsed economiclly but somehow manages to soldier on politically and socially.) There is too much military hardware there. There are too many people there. It would be a mess for everyone in the region (China, Russia, South Korea, Japan).
But there are several realities in the way of unification:
1) The Northern elites don't want it. This is really the biggest problem because until you can get the North to agree to unification there will be no unification. It's essentially impossible to forcedly unify the country. The people of the North have been so indoctrinated to fear everyone from outside the country. And the North's army remains powerful enough to cause so much destruction - not just to the North but to the South as well - that invasion is simply a no-go. You must somehow convince the rulers of the North to give up control to the South.
2) Unification would ruin the South. Unification is expensive. And it takes a long time. You don't just declare a country unified and all is good. You have to build up the poorer partner and work on social unification as well.
The unification of Germany cost upwards of $1.9 TRILLION. And West Germany was a lot richer than South Korea is. And East Germany wasn't nearly as poor as North Korea is. And socially there is still a gap between former East and West Germans. It will take another few generations to create real social unification.
A similar lesson can be learned by looking at Yemen, which was separated between North and South between the end of WWI until 1990. Yet after declaring unification the social separation between the peoples of the two former nations remained and resulted in civil war and unrest which really still continues today. (Equally note that both North and South Yemen were extremely poor nations, which made unification difficult economiclly as well.)
Really, the best scenario would be for the Northern elites to liberalize - open their economy bit by bit and reveal the truth about the rest of the world to their people bit-by-bit. Spend less on the military and more on developing the country - education, infrastructure, and a Chinese-style economic modernization. Then, as the North slowly climbs out of poverty and absolute self-imposed social isolation then maybe in a few decades unification will look more and more realistic.
And really that's what everyone wants. Everyone outside of the Northern elites that is.
There had been some hope that after Kim Jong-il died that his successor would be more open to the rest of the world, but that seems not to be the case.