I know that common font's biggest size is smaller than 72,but my game need more bigger size.How can I do to change my font bigger than 72,or change a special font(but I can't find one witch is bigger than 72)?
I'm able to set Font assets to use any size. I just type it into the size box. As a test, I imported the "Arial Rounded Bold 12" TTF, set its size to 128, clicked apply, and it displayed correctly on screen. On a technical note, true-type fonts are vector-based, so they actually scale-up very well.
Can you clarify as to under what particular conditions you're limited to size=72?
Unity versions prior to 3.0 have fixed textures for the font, so the size is limited depending on the number of characters in the font (which makes it hard to use languages such as Japanese). However Unity 3.0 and later has dynamic font rendering, so there's no practical size restrictions anymore.