用fileSize()函數.
例rocedure TForm1.Button1Click(Sender :TObject);
Var f: file of Byte; size : Longint;
begin
if OpenDialog1.Execute then
begin
AssignFile(f,OpenDialog1.FileName);
Reset(f);
size := FileSize(f);
Edit1.Text := '文件的長度(字節):' + inttostr(size);
CloseFile(f);
end;
end;