Thermal energy storage is a pivotal technology for sustainable energy development and environmental protection. Thermochemical sorption heat storage, including adsorption and resorption heat storage technology, has received great attentions owing to large heat storage density, diversiform working modes and long-term heat storage capacity. The performance of thermochemical resorption heat storage system was measured on the basis of the sorption working pair of MnCl2-SrCl2/NIH3. 3.78 kg and 4.38 kg MnCl2 and SrCl2 composite materials are filled in the sorption reactor. The long-term heat storage potential of thermochemical resorption heat storage system was investigated. The experimental results show the thermochemical sorption heat storage density varies between 398.44 kJ/kg (51.35 kWh/m(3)) composite material and 2027.74 kJ/kg (261.35 kWh/m(3)) composite material under the experimental conditions. The highest thermochemical sorption heat storage density is about 2027.74 kJ/kg (261.35 kWh/m(3)) composite material when charging and discharging temperature is 177 degrees C and 45 degrees C, respectively. The sorption heat storage efficiency ranges from 0.11 to 0.48 under the experimental conditions. The thermochemical sorption heat storage efficiency increases with the increment of charging temperature, whilst decreases with the increase of discharging temperature. The thermochemical sorption heat storage can supply thermal energy with different temperature level and therefore could satisfy miscellaneous requirements of heat users. (C) 2019 Elsevier Ltd. All rights reserved.