<div class="game_introduce">
       <div class="info bg_bor">
        <strong>阿萨德：</strong>
    <div class="howto">
            <ul>
         <li><span class="i_mouseleft">mouseleft</span>阿萨德</li>  </ul>
         </div>
          <p>发生的</p>
</div>     

            StreamReader reader = new StreamReader("c:\\1.txt",Encoding.Default);
            string source = reader.ReadToEnd();
            Regex reg = new Regex(@"(?is)([\u4e00-\u9fa5]+)|((?<=<span[^>]*?>).*?(?=</span>))");
            MatchCollection mc = reg.Matches(source);
            foreach (Match m in mc)
            {
                MessageBox.Show(m.Value);
            }

------解决方案--------------------
C# code
string html = @"
 <div class=""game_introduce"">
       <div class=""info bg_bor"">
        <strong>阿萨德：</strong>
    <div class=""howto"">
            <ul>
         <li><span class=""i_mouseleft"">mouseleft</span>阿萨德</li>  </ul>
         </div>
          <p>发生的</p>
</div>     
";
            foreach (var r in Regex.Matches(html, @"(?<=<span.*?\>)(.*?)(?=\</\s*?span\s*?\>)(.*?)\<\/li\>").Cast<Match>()) {
                string spanval = r.Groups[1].Value;
                string 中文 = r.Groups[2].Value;
            }

------解决方案--------------------
(?i)(?<=<span\sclass="game_introduce"[^>]*?>)[^<>]+(?=</span>)

------解决方案--------------------
        StreamReader reader = new StreamReader("c:\\1.txt",Encoding.Default);
           string source = reader.ReadToEnd();
           Regex reg = new Regex(@"(?is)([\u4e00-\u9fa5]+)|((?<=<span[^>]*?>).*?(?=</span>))");
           MatchCollection mc = reg.Matches(source);
           foreach (Match m in mc)
           {
               MessageBox.Show(m.Value);
           }

------解决方案--------------------
你可以匹配表达式，用协议就可以得到值，但不科学。

------解决方案--------------------
  string html = @"
  <div class=""game_introduce"">
      <div class=""info bg_bor"">
       <strong>阿萨德：</strong>
   <div class=""howto"">
           <ul>
        <li><span class=""i_mouseleft"">mouseleft</span>阿萨德</li>  </ul>
        </div>
         <p>发生的</p>
</div>    
";
           foreach (var r in Regex.Matches(html, @"(?<=<span\s*class\=""i_mouseleft""\s*\>)(.*?)(?=\</\s*?span\s*?\>).*?([^\>]*?)\<\/li\>").Cast<Match>())
           {
               string spanval = r.Groups[1].Value;
               string 中文 = r.Groups[2].Value;
           }

------解决方案--------------------