The invention provides a constant temperature rotary roasting system heated by molten salt and a technology thereof, wherein a molten salt circulating pump is arranged on the upper part of a molten bath, the molten salt circulating pump is connected with a molten salt heater, the molten salt is connected with a drum reactor inlet collection case from the molten salt heater, a drum reactor outlet collection case is connected with the molten bath, a drum reactor heat exchange tube is arranged in the drum reactor, a material inlet of the drum reactor is communicated with a material comminutor, and a clinker outlet and a heat exchanger exhaust port are arranged on the other end of the drum reactor. By continuously and violently tumbling and bumping of the materials in the drum, the system is in favor of heating uniformity of the materials, shortens reaction time, and simultaneously combines a granulation technology to effectively avoid a bonding phenomenon on a wall surface appeared in the material roasting process. by using the molten salt as a heat exchange medium and utilizing good heat stability and high heat transfer coefficient of the molten salt, the technology can well control temperature homogeneity in the drum reactor, to make the product have high extraction efficiency and to make the clinker have good quality.