方法1:
 
<html>
<head>
<title>渐变效果进度条</title>
<script language="javascript">
 var i;
 function go()
 {
  bar_width = document.getElementById("bg").clientWidth;
  i = bar_width;
  setTimeout('start();',300);
 }
 function start()
 {
  if(i-->0)
  {
   ps.style.width = i;
   bn.innerHTML = Math.floor((bar_width-i)/bar_width*100)+"%";
   setTimeout('start();',20);
  }
 }
 
</script>
<style type="text/css">
#bg {
filter:progid:DXImageTransform.Microsoft.Gradient
(GradientType=1, StartColorStr=#FFFF00, EndColorStr=#FF0000);
width:300px;
height:20px;
border:1px solid black;
z-index:0;
position:absolute;
}
#ps {
float:right;
background-color:#FFFF66;
width:100%;
}
#bn {
position:absolute;
text-align:center;
width:100%;
height:100%;
cursor:default;
}
</style>
</head>
<body onload="go();">
  <div id="bg">
    <div id="ps"></div>
    <span id="bn">0%</span>
  </div>
</body>
</html>
 
方法2:
<html>
<head>
<title>渐变效果进度条</title>
<script language="javascript">
var _Hex = Array("00","01","02","03","04","05","06","07","08","09",
"0A","0B","0C","0D","0E","0F","10","11","12","13","14","15","16","17","18","19",
"1A","1B","1C","1D","1E","1F","20","21","22","23","24","25","26","27","28","29",
"2A","2B","2C","2D","2E","2F","30","31","32","33","34","35","36","37","38","39",
"3A","3B","3C","3D","3E","3F","40","41","42","43","44","45","46","47","48","49",
"4A","4B","4C","4D","4E","4F","50","51","52","53","54","55","56","57","58","59",
"5A","5B","5C","5D","5E","5F","60","61","62","63","64","65","66","67","68","69",
"6A","6B","6C","6D","6E","6F","70","71","72","73","74","75","76","77","78","79",
"7A","7B","7C","7D","7E","7F","80","81","82","83","84","85","86","87","88","89",
"8A","8B","8C","8D","8E","8F","90","91","92","93","94","95","96","97","98","99",
"9A","9B","9C","9D","9E","9F","A0","A1","A2","A3","A4","A5","A6","A7","A8","A9",
"AA","AB","AC","AD","AE","AF","B0","B1","B2","B3","B4","B5","B6","B7","B8","B9",
"BA","BB","BC","BD","BE","BF","C0","C1","C2","C3","C4","C5","C6","C7","C8","C9",
"CA","CB","CC","CD","CE","CF","D0","D1","D2","D3","D4","D5","D6","D7","D8","D9",
"DA","DB","DC","DD","DE","DF","E0","E1","E2","E3","E4","E5","E6","E7","E8","E9",
"EA","EB","EC","ED","EE","EF","F0","F1","F2","F3","F4","F5","F6","F7","F8","F9",
"FA","FB","FC","FD","FE","FF");
 function go()
 {
  setTimeout('start();',100);
 }
 var i=0;
 function start()
 {
  if(i++<256)
  {
   ps.innerHTML += "<span style='width:1px;background-color:#FF"+_Hex[256-i]+"00;'>";
   bn.innerHTML = Math.floor(i/2.56)+"%";
   setTimeout('start();',10);
  }
 }
 
</script>
<style type="text/css">
#ps {
background-color:#FFFF00;
width:256px;
margin: 1px;
float:left;
}
#bn {
width:39px;
margin: 1px;
float:right;
text-align:center;
color:#FFFFFF;
font-family:Arial;
font-size:13px;
}
</style>
</head>
<body onload="go();">
<div style="background-color:black;width:300px;height:20px;"><div id="ps"></div><div id="bn"></div></div>
</body>
</html>