In　situ　environmental　transmission　electron　microscope　(ETEM)　could　provide　intuitive　and　solid　proof　for　the　local　structure　and　chemical　evolution　of　materials　under　practical　working　conditions.　In　particular,　coupled　with　atmosphere　and　thermal　field,　the　behavior　of　nano　catalysts　could　be　directly　observed　during　the　catalytic　reaction.　Through　the　change　of　lattice　structure,　it　can　directly　correlate　the　relationship　between　the　structure,　size　and　properties　of　materials　in　the　nanoscale,　and　further　directly　and　accurately,　which　is　of　great　guiding　value　for　the　study　of　catalysis　mechanism　and　the　optimization　of　catalysts.　As　an　outstanding　catalytic　material　in　the　application　of　methane　reforming,　molybdenum　oxide　(MoO3)-based　materials　and　its　deoxidation　process　were　studied　by　in　situ　ETEM　method.　The　corresponding　microstructures　and　components　evolution　were　analyzed　by　diffraction,　high-resolution　transmission　electron　microscopy　(HRTEM)　and　electron　energy　loss　spectrum　(EELS)　techniques.　MoO3　had　a　good　directional　deoxidation　process　accompanied　with　the　process　of　nanoparticles　crushing　and　regrowth　in　hydrogen　(H-2)　and　thermal　field.　However,　in　the　absence　of　H-2,　the　samples　would　exhibit　different　structural　evolution.