The user manual said that I need to
Get the source of xfig (xfig.3.2.5-alpha3.full.tar.gz) and gunzip and untar the file: Either do: gunzip -c xfig.3.2.5-alpha3.full.tar.gz | tar xvf - or gunzip xfig.3.2.5-alpha3.full.tar.gz tar xvf xfig.3.2.5-alpha3.full.tar
It also said that
There is a version of xfig ported to run on the MacIntosh under the Darwin port of XFree86.
But I didn't find how to setup the XFree86 and even the xfig since I am very new to either Mac OS or UNIX.
TeXand related software, so your question is off-topic and likely to be closed. However, the easiest thing to do is install XQuartz and MacPorts. Then, in the terminal, dosudo port install xfig. – Ian Thompson Aug 1 '12 at 23:56