Hi Ziang Chen,
When you say that the 'www' address is not being tracked, do you mean that it's not showing up as a campaign? Or are you saying something different?
I'm not totally sure I understand your problem, but depending on what is actually happening, here are some options that might help:
1) SAINT Classifications: if both URLs are being captured, you can retroactively consolidate both values into one value
2) Processing Rules: this won't help retroactively, but if both values are coming in, you could strip the 'www' so that they match
Please let me know if I'm not understanding correctly.
Thanks!