Smart charging is gaining more attention with the popularity of electric vehicles (EVs). Smart charging which aims only at reducing electricity costs or reducing carbon dioxide (CO2) emissions is efficient in achieving these objectives. However, the times of lower electricity costs and CO2 emissions are not identical in power grids, putting the two objectives in conflict, which may lower the social benefits of EV smart charging. This study investigates the potential social benefit improvement of smart charging by balancing the economy and decarbonization objectives. Considering five regions located in the United States as examples, it is deduced that smart charging balancing economy and decarbonization objectives can reduce the total social costs of EV charging by 14.5%–35.1%. Furthermore, this study analyzes the impacts of three factors on the social benefits change of EV smart charging, namely charging behavior, charger power, and the social costs of CO2. In the context of transport electrification, this study provides important guidance on how to adjust the charging mode of EVs in the future to improve social benefits.