An　in-depth　understanding　of　the　catalytic　reaction　mechanism　is　the　key　to　designing　efficient　and　stable　catalysts.　In　situ　transmission　electron　microscope　(TEM)　is　the　most　powerful　tool　to　visualize　and　analyze　the　microstructures　of　catalysts　during　catalysis.　In　situ　TEM　combined　with　three-dimensional　(3D)　electron　tomography　(ET)　reconstruction　technique　enables　interrogations　of　catalysts＇　structural　dynamics　and　chemical　changes　in　high　temporal　and　spatial　dimensions.　In　this　review,　we　discuss　and　summarize　the　recent　advances　in　in　situ　TEM　together　with　3D　ET　for　catalyst　studies.　Topics　include　the　latest　research　progress　of　in　situ　TEM　imaging　as　well　as　3D　visualization　and　quantitative　analysis　of　catalysts.　We　also　pay　particular　attention　to　artificial　intelligence　(AI)-enhanced　smart　3D　ET.　These　include　deep　learning　(DL)-based　data　compression　and　storage　for　the　analysis　of　large　TEM　data,　recovery　of　wedge-shaped　information　lost　in　3D　ET　reconstructions,　and　DL　models　for　reducing　residual　artifacts　in　3D　reconstructed　images.　Finally,　the　challenges　and　development　prospects　of　current　in　situ　TEM　and　3D　ET　re-search　are　discussed.