<div id="div">

            <span>这是一段话，这是又一段话！</span>

        </div>

            getFull("div");

            function getFull(id) {

                var div = $("#" + id);

                var span = $("#" + id + " span");

                var dWidth = div.width();

                var sWidth = span.width();

                var sl = span.text().length;

                if(dWidth > sWidth) {

                    var cha = dWidth - sWidth;

                    var i = cha / (sl + 1);

                }

                span.css("letter-spacing", i + "px");

                span.css("padding-left", i + "px")

            }