Molecular devices have become an emergent branch of nanoscience and technology beyond traditional silicon-based electronic devices. The properties of these devices are intimately related to the molecular conformation and packing. In this article, three different conformations of melamine molecules are observed on Au(111), and a transition from the lying-down to standing-up phase with long-range order is realized in melamine chains with the assistance of hexabromobenzene (HBB). We argue that it is the expanding of HBB domains from hexagonal to the dimer phase due to surface dehalogenation that facilitates the dehydrogenation of melamine to form a standing-up conformation. Similar transitions are also accomplished on the Ag(111) surface. Our results provide an effective way to achieve standing-up molecular arrays with long-range order on relatively less active metals. This may have significant implications in fabricating organic thin film transistors.