To understand performance of molten salt heat transfer and thermal storage in solar thermal power system, thermodynamic properties of cubic KNO₂ under atmospheric pressure and temperatures between 300 and 725 K are studied with density functional theory combined with a quasi-harmonic Debye model. Temperature dependence of isobaric heat capacity, isochoric heat capacity, entropy, Debye temperature, volume thermal expansion coefficient, equilibrium volumes and bulk modulus under ambient pressure are calculated. It shows that calculated isobaric heat capacities are in good agreement with experiments under ambient pressures. Both entropy vary greatly. The average volume thermal expansion coefficient-is 1.837 8×10^-5K^-1 and Debye temperature is 667.13K at ambient temperatures, respectively.