Drilling tool and whole-course tripping-in method for underground directional drilling fracturing casing pipe

The invention discloses a drilling tool and a whole-course tripping-in method for an underground directional drilling fracturing casing pipe. The drilling tool comprises a reamer bit, a torque transmission casing pipe, a torque transmission shaft body and a guide bit, and the reamer bit is provided with a first through hole; the torque transmission sleeve and the reamer bit are coaxially arranged, the reamer bit is connected to one end of the torque transmission sleeve, a first connecting part is arranged at the other end of the torque transmission sleeve, a key groove and a separation guide groove are formed in the inner wall of the torque transmission sleeve, and the separation guide groove is communicated with the key groove; the torque transmission shaft body is arranged in the first through hole and the torque transmission sleeve in a penetrating mode, a torque transmission piece is arranged on the outer wall of the torque transmission shaft body, a second connecting part is arranged at one end of the to