A method for manufacturing a honeycomb structure forming die including a liquid groove forming step for forming linear processing liquid grooves whose width is smaller than that of the slit, in positions for forming the slits that form the partition walls of the honeycomb structure by subjecting the kneaded clay to extrusion in one side end face as a kneaded clay forming face of a plate-shaped die substrate. An introduction hole forming step for forming introduction holes for introducing the kneaded clay is performed before or after the liquid groove forming step. Slits communicating with the introduction holes are formed by performing comb-like electro-discharge machining by a comb-like electrode where plate-shaped protrusion electrodes, each corresponding to the width of the slit, are disposed in positions including the processing liquid grooves.