In-situ studies of the vibrational characteristics and microstructure evolution of the Na 2 WO 4 ·2H 2 O (sodium tungstate dihydrate) crystal during the temperature-induced solid-state phase transformation and melting process were carried out using high-temperature Raman spectroscopic technique. Results showed that the thermal decomposition process of the Na 2 WO 4 ·2H 2 O crystal takes place mainly within the temperature range of 348-383 K, along with the structure transforming from the orthorhombic to cubic symmetry. As the sample temperature increased further, another solid-state phase transformation from the cubic to orthorhombic structure was observed approximately at 893 K before melting occurred at 1023 K. Although the isolated [WO 4 ] 2− tetrahedron was preserved within the entire temperature range from room temperature to 1023 K, subtle changes were observed with the mean bond length of W-O bonds in the tetrahedron unit. Furthermore, Raman active vibrational modes of Na 2 WO 4 ·2H 2 O, two Na 2 WO 4 crystal phases, and corresponding melt were assigned based on the density functional theory simulation and compared with the literature data. Finally, four-molecule cluster arranged as T d symmetry is considered to be the most likely configuration in the molten state according to density functional theory simulation based on the different multimolecular clusters proposed.