以750宽度为10rem来计算

css代码

@media (min-width: 320px){html{font-size: 42.6667px;} }
@media (min-width: 360px){html{font-size: 48px;} }
@media (min-width: 375px){html{font-size: 50px;} }
@media (min-width: 384px){html{font-size: 51.2px;} }
@media (min-width: 414px){html{font-size: 55.2px;} }
@media (min-width: 448px){html{font-size: 59.7333px;} }
@media (min-width: 480px){html{font-size: 48px;} }
@media (min-width: 512px){html{font-size: 68.2667px;} }
@media (min-width: 544px){html{font-size: 72.5333px;} }
@media (min-width: 576px){html{font-size: 76.8px;} }
@media (min-width: 608px){html{font-size: 81.0667px;} }
@media (min-width: 640px){html{font-size: 85.3333px;} }
@media (min-width: 750px){html{font-size: 100px;} }

js代码

!(function(doc, win) {
    var docEl = doc.documentElement,
        resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
        recalc = function() {
            var clientWidth = docEl.clientWidth;
            if (!clientWidth) return;
            if (clientWidth < 750) {
                docEl.style.fontSize = 100 * (clientWidth / 750) + 'px';
            } else {
                docEl.style.fontSize = '100px';
            }
        };
    if (!doc.addEventListener) return;
    win.addEventListener(resizeEvt, recalc, false);
    doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window);

这两个代码建议在body之前引入，避免出现加载时界面错乱问题