For many years under Mao, China was an isolated country—both economically and diplomatically. This made it much more difficult for the dominance and control of the ruling Communist Party to be challenged. Also, from its inception Chinese Communism was inextricably linked with Chinese nationalism in a way it was not...
in other communist countries. The Chinese Communist Party (CCP) had played a leading role in fighting the Japanese during World War II and so gained a reputation as being an effective defender of Chinese national interests. In the eyes of many, the CCP was the Chinese nation, as prior to World War II there was no independent China.
As the Soviet Union was the inheritor of a multiethnic state that had existed for centuries, there was no automatic identification of the ruling Communist Party with Russian nationalism. Also, it was the various ill-suppressed nationalist tensions within the Soviet Union which helped to bring about its eventual collapse.
Because of its relative isolation, China didn't find itself becoming mixed up in the kind of overseas entanglements that eventually dogged the Soviet Union. The Chinese did intervene in the Korean War, but as that conflict was right on its border; it could be more effectively managed than, say, Soviet involvement in Afghanistan. The Soviet Union also had to maintain effective control over the Eastern Bloc countries, and there was nothing comparable to this in the case of China.
Finally, economic reform in China has been kept strictly in the hands of the governing CCP. Although China has become a rapidly developing capitalist economy over the last thirty years or so, the overall strategic direction of the economy remains firmly under the control of the one party state.