Nitrate molten salt is widely used as an efficient thermal storage material for improving concentrated solar power (CSP) technology, which is due to their many excellent properties such as thermal stability, high energy density, low viscosity and liquefaction temperature. However, it is not convenient to measure the performance of nitrate for a long time in a high temperature molten state, which can cause the storage containers made of stainless steel to be corroded by nitrate salt. Simulations also face huge challenges in optimizing the performance of nitrate molten salts, with models being complex and calculation time being long. In this study, an empirical electron theory (EET) of solids and molecules is used to investigate the valence electron structure, cohesive energy, and melting points of MNO₃ (M = Li, Na, K) and their decomposition byproducts (nitrites) systematically for revealing the mechanisms of these properties. The calculated bond lengths, cohesive energy, and melting points of nitrate molten salt are in agreement with their corresponding measurements. This study reveals the strong dependence of physical properties on the valence electron structure. The bonding strength and ability strongly depend on the covalent electron pairs n_\alpha . The cohesive energy exhibits a positive correlation with the number of valence electrons n_\mathrmc . The melting mechanism originates from the melting-broken M−O (M = Li, Na, K) bond by the vibrating of thermal phonon at melting temperature. It is suggested that the atomic cluster of NO₃ is still stabilized in the melting process. In binary nitrate molten-salts, the calculated liquidus lines match the measured ones in their binary phase diagrams well. The liquid temperatures show significant positive correlation with the weighted average number of covalent electron pairs ( n_M-\mathrmO ) on M−O bond. The thermodynamic simulation models are used systematically to predict the viscosity, electrical conductivity, and thermal conductivity of the binary nitrate molten-salts. Based on the calculations of EET and thermodynamic simulations, the composition of binary nitrate molten salts is optimized as 0.5LiNO₃-0.5NaNO₃, 0.5LiNO₃-0.5KNO₃, and 0.6NaNO₃-0.4KNO₃, which are considered as good candidates for advanced molten salts with high thermal conductivity, high electrical conductivity, low viscosity, and low liquefaction temperature.