Thanks to Athanasios Karagiannis

My codes run well to export RDLC to PDF!

// dump PDF to browser
Warning[] warnings;
string[] streamids;
string mimeType, encoding, extension;
byte[] bytes = ReportViewer.LocalReport.Render("PDF", null, out mimeType, out encoding, out extension, out streamids, out warnings);
Response.Buffer = true;
Response.Clear();
Response.ContentType = mimeType;
Response.AddHeader("content-disposition", "inline; filename=myfile." + extension);
Response.BinaryWrite(bytes);
string pdfPath = Server.MapPath("~") + "pdf." + extension;
FileStream pdfFile = new FileStream(pdfPath, FileMode.Create);
pdfFile.Write(bytes, 0, bytes.Length);
pdfFile.Close();
Response.Flush();
Response.End();