Concentrating Solar Power (CSP) system with storage can provide consistent power and thus are attractive relative to intermittent power sources, e.g., solar photovoltaics and wind. Mixed molten salt is considered as a promising medium for both heat transfer and energy storage in solar thermal power because of its many advantages such as large heat capacity, low vapor pressure, low cost, wide range of temperature in application, etc. However, there are the disadvantages of higher melting point and poor thermal stability with the commonly mixed molten salts, such as Solar salt (60wt%NaNO3+40wt%KNO3, melting point @220℃, limit use of temperature @ 565℃). In order to obtain molten salt with lower melting point and better thermal stability, 16 kinds of mixed molten salts are obtained by adjusting the component radio and adding carbonates or additives based on Solar salt. Through the Differential Scanning Calorimetry (DSC) and Thermogravimetric (TG) methods, their melting point, crystallization point, thermal decomposing temperature and thermal stability are measured. 4 kinds of mixed molten salts are selected preliminarily at last. Their melting points and decomposing temperatures are about 100℃ and 600℃, separately. They show good thermal stability in the four repeated heating-cooling experiments.