The invention relates to a bending device with a movable roller of a cable for transmitting electric power and a bending method. The bending device is used for bending a head part of the cable, so that the shape of the cable is adaptively tightly connected with an electric power device. The bending device comprises a stander, a left slide forming mold and a right slide forming mold, wherein the left slide forming mold and the right slide forming mold are arranged in the lateral direction, movable rollers are arranged at the bottoms of the left slide forming mold and the right slide forming mold, the bottom of each forming mold is provided with two movable rollers, so that the left slide forming mold and the right slide forming mold are driven to move; an upper guide roller pair and a lower guide roller pair are respectively arranged on middle positions of the upper edge and the lower edge of the stander, and a gap between two rollers of the upper guide roller pair and a gap between two rollers of the lower guide roller pair are mutually aligned to each other so as to allow the passing of the cable.