It means something different with different punctuation. The porcelain bodies of luanbai wares have a greater aluminium oxide content than qingbai wares at 20-21 per cent = The qingbai wares have a 20-21 percent content and the luanbai wares have a greater content than that. The porcelain bodies of luanbai wares have a greater aluminium oxide content than qingbai wares, at 20-21 per cent. (note the comma)= The luanbai wares have an aluminum oxide content of 20-21 percent, which is greater than that of the qingbai wares. The sentence would be clearer as: The porcelain bodies of the luanbai wares have an aluminium oxide content of 20-21 percent, which is greater than that of the qingbai wares. (If that is the meaning, of course).

I would say this sentence is poorly phrased even for a native English speaker. However, my guess is meaning number 1 is correct.