how to show leading zero in excel through c#

The best you could do is to convert the column format to Text
That can be done by

In the following I am converting the format of the C1 column to Text

range["C1"].NumberFormat="@";
range["C1"].Value="00129";/*Then you have to specify the value*/  

the above will give the exact value you assigned to the column.

You can also look at the other formats like Pincode, Creditcard number format in the following
http://office.microsoft.com/en-sg/excel-help/keep-leading-zeros-in-number-codes-HA010342581.aspx[^]

The best way to do it is to format the column as a number, with the appropriate number of leading zeros - that way you can still use it as a numeric value.
This creates a new file, with the first column formatted to show two digits, with a leading zero:

Excel.Application excel = new Excel.Application();
excel.Visible = true;
Excel.Workbook wb = excel.Workbooks.Add(1);
Excel.Worksheet ws = (Excel.Worksheet) wb.Sheets[1];
ws.Cells[1, 1].EntireColumn.NumberFormat = "00";
wb.SaveAs(@"D:\Temp\aaexcel.xlsx");

But you can open an existing file instead and apply the formatting in exactly the same way.

Excel.Range formatRange;
formatRange = xlWorkSheet.get_Range("a1", "b1");
formatRange.NumberFormat = "@";
xlWorkSheet.Cells[1, 1] = "098";

Full Source : C# Excel Formatting

Justin