Coal ash fusibility is crucial for boiler and gasifier performance. A study focused on coal ash rich in sodium and sulfur, like Zhundong coal, known for causing slagging issues. Synthetic ashes were created to investigate sodium and sulfur behavior. Results showed that ash fusion temperatures were higher in oxidizing atmospheres. Sodium decreased AFTs in reducing atmospheres by forming fusible compounds, but turned into sodium sulfate in oxidizing atmospheres, leading to lower AFTs. Sodium sulfate formation depended on SiO2 and Al2O3 content. This study provides insights to properly assess ash fusibility and prevent slagging and ash deposition caused by sodium sulfate.