Formaldehyde titration method was used to study the terminal decomposition process of the product of the ammonia method. The concentration variation of main ions was measured when the ammonium bicarbonate solution with initial concentration from 3.0%~7.9% decomposed at 323~363 K. Besides that the determination of the solubility for ammonium bicarbonate in the NH4HCO3?Na2CO3?H2O system from 288 to 313 K was carried by a dynamic method. The results show that the concentration of HCO3? ion falls sharply within the first 30 min and then decreases slowly. The decomposition rate of ammonium bicarbonate solution grows as the temperature rises, at the same temperature the higher the concentration of ammonium bicarbonate solution is, the shorter equilibrium time will be needed. Decomposition process of ammonium bicarbonate solution can be described by the Lageren equation after calculated; It has also been discovered that the solubility of NH4HCO3 increased with the rising of temperature, and increased firstly and then decreased gradually with increasing the concentration of Na2CO3 solution at the same temperature. With a peaked value at Na2CO3 concentration was 0.1 mol/kg when the equilibrium phase changed from NH4HCO3 to NaHCO3 in this aqueous system.