The effects of KNO3 on the thermal reaction characteristics and ignition combustion phenomenon of nano-aluminum powder in CO2 were studied by thermal analysis techniques and visualization tube furnace. The results show that ignition temperature of nano-aluminum powder decreases with the increase of KNO3 concentration, the ignition temperature of nano-aluminum powder with 1%(w) and 5%(w) KNO3 can be reduced by 18.3 and 37.9℃, respectively, and the combustion characteristic index of nano-aluminum powder increases, but the incremental rate gradually declines. Ignition of nano-aluminum powder with addition of KNO3 can be accelerated, so the oxidation of aluminum powder is more violent. Furthermore, the combustion products of nano-aluminum powder with KNO3 not only contain a large amount of a-Al2O3 and a small amount of activated Al, but also have g-Al2O3.