Gallium nitride (GaN) material has become a research hotspot at home and abroad because of its unique properties and application prospects. High quality GaN single crystals are the prerequisite for obtaining optoelectronic devices and power devices with excellent performance. Because of its mild growth conditions, the sodium flux method is easy to obtain high quality and large size GaN single crystals, and it is a promising method for the growth of GaN single crystals. Since the sodium flux method was invented in the late 1990s, the crystals grown by the sodium flux method have made considerable progress in size and quality after more than 20 years of development. Recent research progress of GaN single crystals grown by the sodium flux method from the aspects of crystal growth principle, seed crystal selection, temperature gradient and additives are summarized in this paper, and the challenges and future development trend are also prospected.