$(function(){
     var element = $("div[class='new-comment-content']");
     var temp =  element.text().replace(/\n/g,'<br/>');
     element.html(temp);
});

2.php 


php html自动换行
ereg_replace("\r\n", chr(13), $_POST['content']);

ereg_replace("\r\n", "<br/>", $_POST['content']);