The SrMgF4 powder has been hydrothermally synthesized from the double system. The effects of factors such as the ratio of initial reaction, pH value, reaction temperature and time were investigated. Moreover, the SrMgF4:RE(RE=Eu, Tb) phosphors were prepared by the hydrothermal method. Further, they were characterized by means of inductively coupled plasma atomic emission spectrometer, X-ray powder diffraction, scanning electron microscopy, thermogravimetric analysis, and infrared spectroscopy. The luminescent properties were investigated by the luminescence spectrometer. The results show that the molar ratio and pH in the initial reaction mixture associated with the reaction temperature dominate the crystallization of the products. The products are air stable. SrMgF4:RE obtained was pure phase of SrMgF4. It indicates that doping a low concentration of RE3+ ions couldn’t change the structure. In the co-doped Eu3+ and Tb3+ system, Eu3+, Tb3+ and Eu2+ are observed in one matrix. These phenomena can be explained using an electron transfer theory. These RE ions occupy the sites of Sr2+ in SrMgF4.