A method and a device for keeping an active state of a smart card until re-entering a field, and a smart card are provided. The method includes: sending a waiting time extension instruction by a smart card to an electronic device when the smart card is in an electromagnetic field of the electronic device and in an active state; starting a timer after the smart card receives a reply in response to the waiting time extension instruction; detecting that the smart card leaves the field, determining whether the timer times out, and keeping a current state of the smart card as the active state when the timer does not time out and detecting that the smart card re-enters the field, determining whether the timer times out, and keeping the current state of the smart card as the active state when the timer does not time out.