The invention provides a molten nitrate salt heat transfer and heat accumulation medium. The heat transfer and heat accumulation medium is prepared from potassium nitrate, lithium nitrate and calciumnitrate. The nitrate salt heat transfer and heat accumulation medium disclosed by the invention has a low melting point and can be applied to a solar thermal power generation system; thus, an initialoperation procedure of the system can be simplified, a special heating device for preventing frozen blocking of the molten salt is avoided, safety stability of the whole system is improved, and operation cost of the whole heat transfer and heat accumulation system is simultaneously reduced. A thermal decomposition temperature can reach 588 DEG C or more, so that the highest use temperature of theheat transfer and heat accumulation medium is improved, and the power generating efficiency of the whole system is greatly improved.