>Hi,
>Thank you for your reply,
>but the result still the same.
>
>Is it Excel bug ?

Nope, it's a feature. You may set date in your app any way you want, but Excel has its own expectations about the date format, which mostly means it will read the user's system-level settings and expect dates to be set that way.

Since excel keeps dates as numbers - http://support.microsoft.com/kb/214094 calls them serial numbers. So you could use that:

oExcel = CREATEOBJECT([Excel.Application])
oExcel.SheetsInNewWorkbook = 4
oWorkbook = oExcel.Workbooks.Add()
nrow=2
dateZero=date(1899,12,31)
select invoice
do while !eof()
    with oExcel.activesheet
         .Range("A"+TRIM(PADR(nrow,11))).value=invoice->invno
         .Range("B"+TRIM(PADR(nrow,11))).NumberFormatLocal ='dd mmm yyyy' 	    
         .Range("B"+TRIM(PADR(nrow,11))).value=invoice->invdate - dateZero
   endwith 
   nrow = nrow + 1
   select invoice
   skip 1
enddo

Don't have excel installed (LibreOffice works just fine, thanks) so can't really try this.