1) Maintain central authority over the commercial seaboard and the peasant hinterland
2) Surround itself by a buffer of vassal states on land - Tibet, Sinkiang, Mongolia, Manchuria, etc.
3) Build a strong navy to repel sea-based foreign predation, protect its trade and extend its influence over East Asia. Now and in the future, China is going to have cope with a panoply of threats to those geopolitical goals - rising inequalities, a disconnected bureaucracy, ethnic separatism and American and Japanese sea power. In other words, it's going to have its hands full and Chinese willingness to pursue reconciliation and friendship with Russia is a reflection of its need for a safe strategic rear (see Sino-Russian Relations in China Debates the Future Security Environment, Michael Pillsbury).