More than 30,000 tons of molten salts as efficient heat transfer and thermal energy storage materials have been employed in a single commercial concentrating solar power plant. Nanoparticles could increase the thermal performance of molten salts. However, there is no efficient synthesis method for the mass production of molten salt nanofluids by far. In this work, two techniques that are aqueous solution and high-temperature melting methods, which could be potentially used for the large scale production of molten salt nanofluids, were comparatively evaluated by investigating the thermal performance of solar salt dispersed with 1.0 wt % 20 nm SiO2 nanoparticles. The differential scanning calorimetry, thermogravimetric analysis, and laser flash analysis were employed to analyze the thermal performance of molten salt nanofluids. Results showed that the high-temperature melting method achieved an energy-efficient and much-simplified synthesis process, which was superior to the aqueous solution method for the mass production of molten salt nanofluids. At the same operating conditions, the increases in the latent heat, specific heat, and thermal conductivity of molten salt nanofluids prepared by the high-temperature melting method were 1.2, 28.17, and 35.71% higher than those by the aqueous solution method, respectively. SEM observations indicated that this difference in thermal performance could be related to the micromorphology. In the aqueous solution method, strong natural convection during water evaporation in nanofluid solution induced the agglomeration of SiO2 NPs and hence caused uncertain changes in micromorphology. While in the high-temperature melting method, microcrystal structures around NPs kept their original structures during the cooling process due to the close density of SiO2 NPs and molten salt.