Clean　energy　innovation　has　triggered　the　development　of　single-atom　catalysts(SACs)　due　to　their　excellent　catalytic　activity,　high　tunability　and　low　cost.　The　success　of　SACs　for　many　catalytic　reactions　has　opened　a　new　field　where　the　fundamentals　of　catalytic　property-structure　relationship　at　atomic　level　await　exploration,　and　thus　raises　challenges　for　structural　characterization.　Among　the　characterization　techniques　for　SACs,　aberration-corrected　transmission　electron　microscopy(TEM)　has　become　an　essential　tool　for　direct　visualization　of　single　atoms.　In　this　review,　we　briefly　summarize　recent　studies　on　SACs　using　advanced　TEM.　We　first　introduce　TEM　methods,　which　are　particularly　important　for　SACs　characterization,　and　then　discuss　the　applications　of　advanced　TEM　for　SAC　characterization,　where　not　only　atomic　dispersion　of　single　atoms　can　be　studied,　but　also　the　distribution　of　elements　and　the　valence　state　with　local　coordination　can　be　resolved.　We　further　extend　our　review　towards　in-situ　TEM,　which　has　increasing　importance　for　the　fundamental　understanding　of　catalytic　mechanism.　Perspectives　of　TEM　for　SACs　are　finally　discussed.