The invention discloses a drilling assisting device used for blasting construction of a concrete ledge and a drilling method thereof. The assisting device includes an auxiliary positioning rod and a fixation rod used for fixing the relative position of the auxiliary positioning rod and the concrete ledge, the fixation rod is arranged on the auxiliary positioning rod, and the fixation rod is perpendicular to the axis of the auxiliary positioning rod; and a row of guide holes uniformly distributed in the axial direction and corresponding to to-be-drilled positions are formed in the auxiliary positioning rod. The drilling assisting device used for blasting construction of the concrete ledge has the advantages of being simple in structure, rapid and efficient to use and capable of improving the drilling accuracy and the like. The drilling method has the advantage that the drilling assisting device can be efficiently and rapidly used for drilling.