This paper describes the calibration method and the calculation equations of expanded uncertainty for a precision electric force measuring device. The calibration of the electric force measuring device is performed three times (0 ${circ}$(first time), $120{circ}$(second time), $240{circ}$(third time)) at each calibration point. It is usually selected ten points from zero load to rated load of the electric force measuring device. The expanded uncertainty is calculated by combining A type standard uncertainty and B type standard uncertainty. The calibration method and the calculation equations of expanded uncertainty can be widely used in the calibration of the precision electric force measuring device.