The Low Point of China is located at Lake Ayding which is a dry yet muddy Lake 154 m below sea level.  The Lake is located in the Turpan Depression (or Turfan Depression) in the far western part China.  The Turpan depression is the third lowest depression, after the Dead Sea Depression and the Afar Depression.
For more information refer to the following links:

The image above was obtained with permission from wikipedia and shows a Monument marking the lowest altitude point in China.  There is a good chance that this photo is a fake. Hopefully one day we will be able to visit this location.