一

<script>

(function (doc, win) {

var docEl = doc.documentElement,

resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',

recalc = function () {

var clientWidth = docEl.clientWidth;

if (!clientWidth) return;

docEl.style.fontSize = 20 * (clientWidth / 320) + 'px';

};

if (!doc.addEventListener) return;

win.addEventListener(resizeEvt, recalc, false);

doc.addEventListener('DOMContentLoaded', recalc, false);

})(document, window);

</script>

二

<script>

var scale = $('body').width() / 640;

$('html').css('font-size', 100 * scale + 'px');

</script>

三（使用过的）

<script>

var fontSize = 100;

var elm = document.documentElement;

elm.style.fontSize = fontSize * (elm.clientWidth/320) + 'px';

</script>