The liquidus temperature of molten salt NaCl-KCl-NaF-Na2WO4 system was measured by differential thermal analysis. The results show that in the molten salt system when 0.6 eutectic temperature is 542.1 °C and a phase transition temperature is 515.4 °C, eutectic composition become = 0.28, = 0.28, =0.14, = 0.3; when > 0.6, eutectic temperature and a phase transition temperature are respectively 597.7 °C and 495.8 °C, eutectic composition become = 0.12, = 0.12, = 0.06, = 0.7.