I found that the problem was caused by another old copy of TikZ. Specifically, I installed TeXLive 2014 at
C:\texlive, but there is a folder called
C:\Users\<username>\texmf\tex\latex where I had put user-defined library or templates.
I think sometimes ago, when I first try to use TikZ, I downloaded the old TikZ there (because I didn't know TeXLive already included it). It seemed that this user path has higher priority than the installation one. After deleting TikZ in the user path, everything worked again.
So from this, my recommendation is that if you want to install some library, you'd better check TeXLive manager first. There might be already something you want, and you can just update there instead of downloading by yourself and cause some inconsistency problem like mine.