Solid solutions with different compositions, mNH4Cl·KCl and NH4Cl·nKCl (m，n≥1), were prepared by the constant speed cooling method. The thermal stability of the solid solutions was determined by TG-DTA. The results show that mNH4Cl·KCl crystals change its crystal form at 180°C, decompose into ammonia and hydrogen chloride gas at 330°C, melt at 790°C, and finally evaporate at around 820°C. Its evaporation temperature increases with the increasing of potassium chloride content in the samples. The Solid solution of NH4Cl·nKCl decomposes to ammonia and hydrogen chloride gas at 230°C, melts at 790°C, and evaporates at 800°C. The continuous specific heat curve of the solid solution (NH4, K)Cl were also determined. These data provide a theoretical basis for further research on solid solution properties.