public void OpenReportTempalte()
{
if (m_oExcelApp != null)
CloseReportTemplate();

m_oExcelApp = new ApplicationClass();
//new workboos
Books = (Excel.Workbooks)m_oExcelApp.Workbooks;

Book = Books.Open(sReportTemplate, m_oMissing, m_oMissing,
m_oMissing, m_oMissing, m_oMissing, m_oMissing, m_oMissing, m_oMissing,
m_oMissing, m_oMissing, m_oMissing, m_oMissing);
sheets = (Excel.Sheets)Book.Worksheets;
worksheetSheet = (Excel.Worksheet)sheets.get_Item(1);
cell = (Excel.Range)worksheetSheet.Cells.get_Range("A1", "A1");

cell[1, 1] = "Mobileno";
Excel.Range cellrange = (Excel.Range)cell.get_Resize(20000, 1);
Book.Worksheets.Add(m_oMissing, m_oMissing, m_oMissing, m_oMissing);
cellrange.NumberFormat = "0";
body = (Excel.Range)worksheetSheet.Cells.get_Range("B1", "B1");
body[1, 1] = "StatusDate";
Excel.Range bodyrange = (Excel.Range)body.get_Resize(20000, 1);
bodyrange.NumberFormat = "m/d/yyyy";


}
and
fill data from dataset with this code

OpenReportTempalte();

// Get employee data
DataSet oRptData = new DataSet();
SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.AppSettings["sqlcon"]);
con.Open();

string strp = "Select Top 2 * from BillingSMSMessages where ClientId=188";
SqlCommand com = new SqlCommand(strp);
com.CommandText = strp;
com.Connection = con;
com.CommandType = CommandType.Text;
SqlDataAdapter adp = new SqlDataAdapter(com);
adp.Fill(oRptData);
int nRow = 2;


foreach (DataRow oRow in oRptData.Tables[0].Rows)
{
worksheetSheet.Cells[nRow, 1] = oRow["SM_MobileNo"];
worksheetSheet.Cells[nRow, 2] = oRow["SM_StatusDate"];
nRow++;
}
if (File.Exists(vpath) == true)
{
File.Delete(vpath);
worksheetSheet.SaveAs(vpath, m_oMissing, m_oMissing, m_oMissing, m_oMissing, m_oMissing, m_oMissing, m_oMissing, m_oMissing);
sReportFile = vpath;
}
else
{
worksheetSheet.SaveAs(vpath, m_oMissing, m_oMissing, m_oMissing, m_oMissing, m_oMissing, m_oMissing, m_oMissing, m_oMissing);
sReportFile = vpath;
}
System.GC.Collect();