返回服务器相应目录文件列表，检查下文件列表，有相同文件则不重传，或者检查服务器上的文件大小，如果和实际的不相符可以覆盖.....

procedure TForm1.Button1Click(Sender: TObject);
var
aDirList: TStringList;
aServerDir: string;
aYourFile: string;
finded: boolead;
begin
IdFTP1.User := '';
IdFTP1.Password := '';
IdFTP1.Host := '';
IdFTP1.Port := ;
IdFTP1.TransferType := ;
IdFTP1.Connect();
IdFTP1.ChangeDir(aServerDir);
aDirList:= TStringList.Create;
finded := True;
try
IdFTP1.List(aDirList, aYourFile, False);
except
finded := False;
end;

if finded then
begin
Memo1.Lines.Assign(aDirList);
end
else
begin
Memo1.Lines.Add('can not find');
end;
aDirList.Free;
end;