Abstract: Based on the TG-DSC analysis for the thermal decomposition of ammonium metavanadate（NH₄VO₃,AMV for abbreviation） in air,The phases of the final products for the thermal decomposition of AMV in air and the morphologies of the pyrolysis products of AMV at the inflection point temperatures in corresponding DSC curve were characterized by X-ray diffraction （XRD） and scanning electron microscope （SEM）,respectively.The results show that there are two steps in the thermal decomposition process of AMV in air.There is （NH₄）₂O·2V₂O₅ as mediate phase during the first step,and the transition from amorphous to crystal state of the pyrolysis products of AMV in air happens in the second step. The morphologies of the pyrolysis products of AMV in air are mainly irregular flakes in different periods,but the thickness of vanadium pentoxide （V₂O₅） is relatively homogeneous.