不知你看过Delphi帮助没有：
FileSize returns the size of a file in bytes or the number of records in a record file.
Note
FileSize can't be used on a text file.
不过你可以用下面函数实现：
function FileLength(Filename:string):integer;
var
fp:file of byte;
begin
AssignFile(fp,Filename);
Reset(fp);
Result := FileSize(fp);
CloseFile(fp);
end;
