Growing interest in homoepitaxial growth of nitride-based devices has driven considerable efforts towards producing bulk gallium nitride single crystal as a substrate for the devices. Therefore, the process of producing the bulk gallium nitride crystal substrate should be simple and yet cost-effective to reduce the production cost of the devices. To date, several methods of growing bulk gallium nitride crystal have been proposed. Sodium-flux method is one of the most promising ways since it requires a moderate growth temperature and growth pressure, as well as being simple and cost-effective. This paper will briefly review the progress made to advance the growth of bulk gallium nitride single crystal by sodium-flux method, including discussing challenges and proposing possible improvements in future.