In this study, the sodium emission and control with firing a high-alkali coal was investigated in a high-temperature muffle furnace. Kaolin was chosen as an additive tested to clarify its sodium capture mechanism and assess its capture performance. The influence of some firing-related factors, such as kaolin dosage, temperature, and particle sizes, of both kaolin and coal on sodium release and sodium capture performance of kaolin was also studied. It was found that more sodium was released when the combustion temperature rose or fine fuel particles were combusted. Kaolin could efficiently capture sodium species to form high-melting sodium aluminosilicates, primarily nepheline or carnegieite. Increasing kaolin dosage led to the promoted sodium retention. However, the promotion was not that pronounced in high kaolin dosages. High temperature had a negative effect on sodium capture by kaolin, which could be ascribed to the increasing sodium emission with temperature. Fine kaolin particles exhibited a good sodium capture performance. Coal particle size had little impact on the interactions between kaolin and sodium species. More than 80% of the total sodium was retained in ash by kaolin when firing coal (30 mu m) with 3 mu m kaolin addition in the dosage of 6 wt% at 1100 degrees C.