The energy of explosion of aluminized explosive with two particle size in vacuum and 1 atm were messured by isothermal calorimeter, and the influence rules of Al powder granularity and explosion atmosphere on the reaction rate of Al powder were calculated. The results show that the reaction content of Al powder increases in both vacuum and 1atm atmosphere with the increase of Al powder content in aluminized explosive. In vacuum atmosphere, when the content of Al powder is 5%~30%, the reaction rate of 12μm and 125μm Al powder both are 33%~38%. When the content of Al powder is 35%, the reaction rate of which are 36.4% and 29.7% respectively, and the downtrend of the reaction rate of 12μm Al powder is evident; In 1atm atmosphere, when the content of Al powder is 5%, the numerical value of reaction rate of Al powder is highest, which of 12μm and 125μm Al powder are 75% and 56% respectively. When the content of Al powder is 10%~35%, that are 40%~47% and 45~51% respectively.