You can't transfer your Chinese visa on your old passport to your new passport, the Chinese embassy doesn't provide this service, when you go to China, you can take your old and new passport together, then the Chinese visa can still be used.

When renew passport, the old passport will cut off a corner. Will the old passport still valid?

Ms. Wong, I haven't faced such a thing, but I read an answer by Mr. Alan Paul who said that aliens can use the visa on the old passport together with the new passport. To be safe, you can apply for a new Chinese visa on your new passport. You can call the Chinese embassy in Singapore to enquire it, if you have more information, can you post it here to share with me? Thanks in advance!