By means of an automated laboratory reactor with reaction calorimetry SIMULAR,the reaction heat and factors affecting synthesis of 5-aminotetrazole by the Stolleet′s method was studied. The results show that the reaction heat of 5-aminotetrazole is 130.35 kJ·mol^-1. The most befitting quantity of nitric acid is equimolecular. The pH value of reaction should be 2.5～5.5. The most economic reaction time is 120 min. There is a violent exothermic reaction peak in the finishing period,the instantaneous reaction heat reaches to 65 W.