I have installed the font programmatically and I can see the font in Windows Font directory, however, when I try to get the font via：
var fontName = app.textFonts.getByName("SourceHanSansCN-Bold")
That expression should get you the font object (although still not null). This should get you the font name:
var fontName = app.textFonts.getByName("SourceHanSansCN-Bold").name;
Did you install the font "For all users"?
yeah, I put the font to the "C:\windows\Font" directory.
can you see the font in the Illustrator UI?
If ExtendScript can't access the font object, you would have gotten an error ("no such element found" or something to that effect). If you're really getting "null", there is more to this than we are being told.