As everybody already said, depends alot on what you mean by "surviving" and "civilization". China's strong contender as long as you don't demand that they've never been conquered by foreigners.
Now, there are conquests and conquests. The Mongol and Manchu conquests of China certainly meant that political power passed out of native hands, but the supremacy of Chinese culture, language and bureaucracy wasn't affected. By contrast, the old Mesopotamian culture was eventually absorbed into Islamic culture, altho' only a full thousand years after the last native ruler (Nabonid) got booted out by the Persians.
The place that's been "civilized", ie had cities, writing etc, the longest is Mesopotamia.