Is there always turbulence over China? I'm not sure if this is appropriate to Aviation.SE, so apologies in advance if not.

I have taken several domestic flights over mainland China (as in, the People's Republic thereof) and, so far, it has always been a bumpy ride. I'm more familiar with flying (as a passenger on a commercial airline) around Europe and, to a lesser extent, the US and don't recall it ever being that bad. Likewise, the trip from Europe to China is reasonably stable.

Is there something about the weather or the terrain in that part of the world that causes this? (This, anecdotally, appears to apply both to flights across China, over the mountainous regions, as well as along the relatively flat eastern seaboard.) Or have I just been unlucky?
China is well known for having very strict air traffic control, who often are reluctant to give pilots the flexibility to deviate around bad weather or try a different - smoother - flight level (as I've experienced first-hand). That can lead to aircraft in Chinese airspace encountering more turbulence than in other parts of the world.

Secondary to that, China can get some nasty weather: Particularly in the South. Compared to Europe they'll have more thunderstorms, for example, and that can lead to increased turbulence. This image here gives an overview of the number of lightning strikes around the globe. Aside from a few patches in Italy, China has more lightning - and hence more turbulence due to thunderstorms - than anywhere in Europe. As you mention, the mountainous terrain in some parts of the country also has an effect, although you get that in Europe too.