With energy consumption for heating areas increasing, the application of solar energy has become more and more widespread in recent years. However, shortages due to discontinuity and weak guarantee rates are the main limitations of solar energy. The aim of this study is to define and validate a new heat storage system with an ammonia water resorption heat pump based on concentration difference, which would improve the utilisation range and time of solar energy in heating areas. The system can be divided into two parts: one is for heat storage in day time, while the other part is working for heating at night. A theoretic model is established and analysed based on thermodynamics and properties of ammonia water. The results of the simulation show that the coupled working pressure ranges (the high pressure and low pressure of the system) are determined by the given temperature of the absorbers and generators in the cycle. With optimising the pairs of the pressure in the given condition (the high/low pressure generator/ absorber of 90°C, 45°C, 40°C and 5°C), an acceptable pair of working pressure is carried out (1.5Mpa/0.48Mpa), and the coefficient of performance (COP) could reach about 1.51, while the energy storage density (ESD) could also reach about 54kwh/m3.