var

  Form1: TForm1;

implementation

{$R *.dfm}

uses

  ShlObj;

function MakeUniqueFileName( const APath, AFileName: string ): string;

var

  UniqueName: array[0..MAX_PATH-1] of Char;

begin

  Result := IncludeTrailingPathDelimiter(APath) + AFileName;

  if FileExists( Result ) then

    if PathMakeUniqueName( UniqueName, Length(UniqueName), PChar(AFileName), nil, PChar(APath) ) then

      Result := UniqueName;

end;

procedure TForm1.Button1Click(Sender: TObject);

var

  FileName: string;

begin

  FileName := MakeUniqueFileName( 'D:\', '123.txt' );  // 如果 123.txt存在 则 123(1).txt

  ShowMessage( FileName );

end;

来源：http://yypbd.tistory.com/1350?category=401325