问无法追加或发布CKEditor值

EN

<textarea name="Description" id="Description" rows="10" cols="80">
    This is my textarea to be replaced with CKEditor.
</textarea>

<script>
CKEDITOR.replace('Description',
{
    filebrowserBrowseUrl: '/....',
    filebrowserUploadUrl: '/....'
});
</script>


function insert(event) {

    event.preventDefault();

    var desc = CKEDITOR.instances['Description'].getData(); //I obtain the updated text at this line
    var formdata = $('#frmCreate').serialize(); 

    formdata.append("Description", desc); //!!! This is not working !!!  

    $.ajax({
        type: "POST",
        url: '@Url.Action("Insert", "Blog")',
        cache: false,
        dataType: "json",
        data: formdata,

        success: function (response, textStatus, XMLHttpRequest) {
            $('#result').html(data);
        }
    });
};