Shall I quit academia or continue doing research without too much luck? My first three year postdoc was almost over and no good publications came out. The thing is that my carefully crafted papers are getting rejected again and again by decent journals (not that good ones). Knowing how bad the academic job market is now, I have a feeling that I may not make it in academia. I could do another postdoc after my 3 year contract or probably choose to quit. 

If I am bad at research, I would quit now for sure. It is just that somehow my mentor has been supportive of me staying in academia and she is very famous. She can't be too wrong, right? Also, I got many projects going well. I think I am pretty good at research. I hope one of those projects will end up in a good journal.  But, it has been three years after my phd.

I came to Europe to do a phd as a poor Chinese guy. At the time, I didn't know much about English and only learned my current major though a 3 year master program in China. I worked hard and learned fast to catch up. But, things just wouldn't click. I did my job but the journals just wont accept my papers. Bad luck? probably. Or, something wrong with my topic or approaches.

If I do another postdoc, I will be way over 30. My life already suffered from my research career. A lonely Chinese guy in a foreign country. No money. No nothing. Just my research. Another postdoc without much hope of making it in academia could cause damages to my life, from which I may never recover. 

Shall I finish more projects and try my luck to do another postdoc ? Or just quit, even though people say i am good. Being good isn't very useful in academia I guess. Only papers count.
You write "My life already suffered from my research career." This is worrying.
Think about this: what do you need the most for a satisfying life? Is it being close to home? Having a fulfilling relationsship? Having a garden? Living in China? Living near the sea? Being a researcher? Find out what it is for you and focus at first on that. Then find out what else you can do while realising your first priority.

Don't get too hung up on Academia. Being a researcher is not a higher calling from some God, at the end of the day it's just a job. There are many good and satisfying jobs out there. Find out what else the world has to offer.