Abstract: Absorption heat pump (AHP) system is an energy-saving technology that utilizes renewable energy or industrial waste heat for refrigeration and heating. Therefore, it has attracted much attention for use in residential and industrial buildings. The thermodynamic performance of the AHP system greatly depends on the thermodynamic properties of its working pairs. In commercial applications, LiBr/H₂O is usually used as a traditional working pair. However, its shortcomings of easy crystallization and severe corrosion have significant impacts on the practical application of high-temperature AHP systems. To overcome the shortcomings of LiBr/H₂O, various ionic liquids (ILs)/H₂O mixtures have been recently investigated as alternative working pairs. Though ILs/H₂O has a wider operating temperature range and less corrosiveness, ILs/H₂O working pairs generally have very high viscosity, which restricts its practical applications. To further solve the above shortcomings of LiBr/H₂O and ILs/H₂O, a new ternary working pairs LiBr-BMIMCl/H₂O was proposed in the previous study. Compared to the traditional LiBr/H₂O binary working pair, the LiBr-BMIMCl/H₂O ternary working pair has advantages in terms of crystallization temperature and corrosiveness. LiBr-BMIMCl/H₂O shows a great potential in the practical application of an AHP and refrigeration systems, especially at a high temperature. Based on the previous study, in this work, several important thermodynamic properties, including densities, viscosities, specific heat capacities, and specific enthalpies were systematically measured and correlated using the least-squares method, and the average absolute relative deviation (AARD) between the measured data and the calculated data is 0.03%, 1.10%, 0.29%, and 0.01%, respectively. In addition to the crystallization temperature and corrosiveness, viscosity is another key thermodynamic property affecting the practical application of working pairs in AHP system. The viscosity of LiBr-BMIMCl/H₂O is less than 25 mm²·s^-1, which is well compatible with the application requirement. Moreover, the addition of LiBr inBMIMCl/H₂O is beneficial for improving the high viscosity of ionic liquids.