先看效果

代码

<style>.alert-sec-circle {stroke-dasharray: 735;transition: stroke-dashoffset 1s linear;}
</style><div style="width: 110px; height: 110px; float: left;"><svg style="width:110px;height:110px;"><circle cx="55" cy="55" r="40" fill="#FFF" stroke="#F4F1F1" stroke-width="6"></circle><circle id="js-sec-circle" class="alert-sec-circle" cx="55" cy="55" r="40" fill="transparent" stroke="#43AEFA" stroke-width="6" transform="rotate(-90 55 55)" style="stroke-dashoffset: 0;">&gt;</circle><text style="font-size: 14px;" x="35" y="50" fill="#BDBDBD">倒计时</text><text x="35" y="68" fill="#ff0000" id="show_clock" style="font-size: 14px;">00:00</text></svg>
</div><script src="http://code.jquery.com/jquery-2.1.4.min.js"></script>
<script>function padToTwoDigits(n) {return String(n).padStart(2, '0');}function show_clock(time) {var m = parseInt(time / 60);var s = time - m * 60;if (m < 0) {m = 0;}if (s < 0) {s = 0;}var show = padToTwoDigits(m) + ":" + padToTwoDigits(s);$('#show_clock').html(show);}function djs(sj, red_sj) {var jsc = $("#js-sec-circle");var span = parseFloat(252 / (sj));var itv;itv = setInterval(function () {show_clock(sj);r = (sj - 1) * span - 252;jsc.attr("style", "stroke-dashoffset: " + r + ";")if (r < -red_sj * span) {jsc.attr("stroke", "red");}if (r < -252) {clearInterval(itv);}sj = sj - 1;}, 1000);}djs(5, 2);</script>