using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string HTMLBody = @"<a href=""read-htm-tid-4546.html"" id=""a_ajax_4546"">今后转移工作重点</a>
<a href=""read-htm-tid-7969541.html"" id=""a_ajax_7969541"">检讨书一份</a>";
            foreach (Match m in Regex.Matches(HTMLBody, @"id\=""a_ajax_(\d+)"">(.+?)</a>"))
            {
                Console.WriteLine("id {0} text {1}", m.Groups[1].Value, m.Groups[2].Value);
            }
        }
    }
}

------解决方案--------------------

try...

C# code
MatchCollection mc = Regex.Matches(yourStr, @"(?is)<a href=""read-htm-tid-(?<number>[^.]+)\.html""[^>]*>(?<title>.*?)</a>");
string[] result = new string[mc.Count];
for (int i = 0; i < mc.Count; i++)
{
   result[i] = mc[i].Groups["number"].Value + "," + mc[i].Groups["title"].Value;
}
//测试代码
foreach (string s in result)
{
   richTextBox2.Text += s + "\n";
}
/*-----输出-----
4546,今后转移工作重点
7969541,检讨书一份
*/