Abstract: Na₂CO₃ was added into coal ash with the amount of 20% which was converted into the weight of Na₂O. Then the mixed coal ash samples were sintered under different temperatures. To explore the transition mechanism of sodium compounds in the sintering process, the EDS elemental analysis method and XRD phase analysis method were used to analyze the sintered ash samples. Then chemical thermodynamic equilibrium calculations were carried out on the basis of EDS analysis results with the Equilib module of the Fact sage 5.2 software. And the results were compared with those of the experiment. Results show that sulfur enrichment will occur as the elevating of temperature. Sodium mainly reacts with sulfur to compose Na₂SO₄. At the same time NaCl occurs, and it will react with the potassium compounds to generate KCl. NaCl, KCl and Na₂SO₄ react with other substances to produce low temperature eutectics.