A manufacturing method of a tire forming mold in which an annular mold portion is constituted by a combination of sectors includes a step of manufacturing a circular arc shaped inner segment provided with a concavo-convex shape, a step of dividing the inner segment by a non-flat surface division so as to obtain a first segment piece and a second segment piece, and a step of incorporating the first segment piece into an inner peripheral side of a back segment of one sector out of a pair of sectors which are adjacent to each other in the tire circumferential direction, incorporating the second segment piece into an inner peripheral side of a back segment of the other sector, and arranging the non-flat surface divided surface in an end surface of the sector.