An electric soldering iron comprises a power unit connecting the electric soldering iron to an external power source, an electric soldering iron body comprising an iron head and a motion sensor for detecting motion of the electric soldering iron body, and a control system connected to the power unit and the electric soldering iron body, which comprises a switch, a control unit and a timer. The control unit directs the switch to maintain or terminate connection between the power unit and the iron head based on motion detected by the motion sensor and duration measured by the timer. When the duration exceeds a predetermined value, the control system enables the switch to terminate connection of the iron head and the power unit to achieve automatic cutoff of power.