Thermal decomposition of NEPE propellant containing hexanitrohexaazisowurtzita (HNIW) was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). The results show that when RDX was replaced by HNIW by half in the propellant, the mass loss of nitric esters mainly took place from 80 ℃ to 145 ℃. Furthermore, when the temperature went up to 145 ℃, RDX and HNIW influenced each other for their thermal decomposition with a major exothermic peak appearing in DSC curve. When RDX was replaced by HNIW totally in the propellant, the mass loss between 145 ℃and 240 ℃ was split in two steps, i.e. decomposition nitric esters and partial decomposition of HNIW. This phenomenon fully shows that the incorporation of nitric esters greatly affects thermal decomposition of HNIW.