//你可以这样用richTextBox1.Lines;把你要删除行的索引找到就行了
string[] sLines = richTextBox1.Lines;
string[] sNewLines = new string[sLines.Length - 1];
Array.Copy(sLines,1,sNewLines,0,sNewLines.Length);
richTextBox1.Lines = sNewLines;
http://topic.youkuaiyun.com/u/20120307/00/c64a771d-0400-405e-9512-f717a90a52b7.html?28270