Thanks a lot.  I found another way:

   var editor1 = document.getElementById('CE_Editor_ID');
   //Get the editor selection
   var editor1doc = editor1.GetDocument();
   if (editor1doc.selection=="Text")
   {
     selectedhtml = editor1doc.selection.createRange().htmlText;
     alert(selectedhtml);
   }

However function PasteHTML(html) helps only if I want to replace the whole HTML text in editor. How about "replace selected text with my own"? Thank you in advance.