CuI was fabricated by an elementdirectreaction route at 40 ℃ in ethylene glycol as solvent, copper powder as oxidant, iodine as reducing agent. The product was characterised by Xray diffraction (XRD) and scanning electron microscopy (SEM). The catalytic activity was reviewed as a catalyst in the thermal decomposition of ammonium perchlorate. The result show that CuI nanoparticles is sheet strcture, its average diameter is about 99 nm at 40 ℃ and its average diameter is about 87 nm at 60 ℃. Addition of CuI in ammonium perchlorate (AP) led to a significant reduction of low decomposition temperature and high decomposition temperature of AP, two decomposition temperture peaks incorporate a decomposition temperture peak, and the temperature of the peak at the high decomposition temperature stage is therefore decreased by 111 ℃. 