The invention discloses a broaching device with a large-diameter double-orientation drill bit and a broaching method thereof. The problems that an existing broaching device cannot achieve successful broaching at a time and broaching centering is difficult are solved. The broaching device comprises a drilling rig drill rod (13) which is connected with the top end of a broaching drill bit center shaft (1) through a connector (2). The broaching drill bit center shaft (1) is sequentially provided with a broaching rear guide cylinder, a broaching bit leg (7) used as a broaching tool and a broaching front guide cylinder from top to bottom. The diameter of the outer circle profile of lower guide ribs (11) in the up-down direction, which are arranged on the outer side face of a broaching front guide winding drum (10), is equal to the pore diameter of a drill hole (14). The diameter of the outer circle profile of upper guide ribs in the up-down direction, which are evenly distributed on the outer side face of a broaching rear guide winding drum (5), is equal to the excircle diameter of the broaching bit leg (7). The broaching device with the large-diameter double-orientation drill bit and the broaching method thereof have the advantages of being high in drilling efficiency, good in broaching centering effect, clean in hole bottom and small in broaching drill bit abrasion.