Single-atom　catalysts　(SACs),　with　100%　atomic　efficiency　and　distinctive　electronic　properties,　show　excellent　catalytic　performance　for　CO2　reduction　to　oxygenates.　However,　the　electronic　structure　of　active　sites　and　key　intermediates　undergo　continuous　changes　during　the　reaction　on　SACs.　It　is　challenging　to　explain　these　phenomena　through　structure-activity　relationship.　Herein,　the　＂electronic　behavior＂　elucidates　the　dynamic　nature　of　electronic　interactions　between　active　sites　and　key　intermediates.　In　this　review,　we　invesitgate　the　transformation　of　the　electronic　structure　within　the　CO2　molecule　and　the　active　site　of　SACs　during　CO2　activation,　elucidating　the　complex　interplay　between　these　two　entities.　Then,　we　delve　into　the　electronic　change　processes　involved　in　thermal,　electro-,　and　photo-catalytic　CO2　conversion,　providing　in-depth　discussions.　Additionally,　the　influence　of　the　catalyst＇s　electronic　behavior　on　the　structure-activity　relationship　is　delineated　with　precision.　At　last,　the　challenges　and　future　perspectives　of　electronic　behavior　for　SACs　are　outlined.