<img onclick="return 1;" />
<a onmouseover="fu_te();" >测试</a>

            string str = @"<a onload=""alert();"" >a onload=""alert();""</a>
<img onload=""dsdfsf();dfsfs();"" /> onload=""alert();""
<div onload=""sf()"" onmousermove=""sdfsfwe();"">sf onload=""alert();"" sf </div>";
            string result = Regex.Replace(str, @"(?is)(?<=<\b[^\s]+\b[^>]*?)\bonload=""[^""]+""(?=[^>]*?>)", "");
            Console.WriteLine(result);
/*
<a  >a onload="alert();"</a>
<img  /> onload="alert();"
<div  onmousermove="sdfsfwe();">sf onload="alert();" sf </div>

*/