In this paper, the thermal decomposition processes of KDN were investigated by means of thermal analysis and FT-IR with in situ cell. The results show that the decomposition of KDN in solid state is different from that of liquid state. The main condensed phase product of the decomposition in solid state is KNO3. While the decomposition of liquid state form KNO3 and KNO2 simultaneously. The possible mechanism of the thermal decomposition in solid state has been proposed. A eutectic can be formed by product KNO3 with KDN. The eutectic temperature of KNO3/KDN system is about 109 degrees C. Moreover another eutectic system can be formed by KNO3 with KNO2 to be eutectic temperature of about 315 degrees C.