In this experiment, it is found that the decomposition reaction of hexamine aqueous solution by heat is the pseudo first order reaction and the calculated decomposition velocity constants of Hexamine aqueous solution are 1.17 * $10^{-5}min.^{-1}(60{deg}$ C), 1.99 * $10^{-5}min.^{-1}(70{deg}$ C), 2.35 * $10^{-5}min.^{-1}(80{deg}$ C), 6.63 * $10^{-5}min.^{-1}(100{deg}$ C). In the result, the activation energy of decomposition reaction of hexamine aqueous solution is 12 $Cal.mole^{-1}.$