The invention relates to a heavy-caliber flange lifting tool and a heavy-caliber flange lifting method. The lifting tool comprises a lifting plate, wherein a lifting ring used for lifting is arrangedat the first end of the lifting plate; a cylindrical pin used for being in matching connection with a bolt hole on a flange is arranged at the second end of the lifting plate; a pressing mechanism isarranged on the lifting plate; and the pressing mechanism is arranged between the cylindrical pin and the lifting ring. When the flange is lifted, the cylindrical pin penetrates into the bolt hole onthe flange, and then the flange is pressed and fixed to the cylindrical pin through the pressing mechanism. According to the heavy-caliber flange lifting tool and the heavy-caliber flange lifting method, the cylindrical pin is inserted into the bolt hole on the flange, the bolt hole on the flange is used as a fixing point, the flange is fixed by virtue of the self weight of the flange and pressingforce of the pressing mechanism, vertical lifting is realized by virtue of the self weight of the flange during lifting, and thus the flange is conveniently lifted to be connected with a pipeline ina pair mode. The lifting tool is simple and rapid to install and dismantle when lifting the flange, and the safety is high during lifting.