To provide a mold data preparation method, a mold manufacturing system, and a recording medium capable of preparing mold data and manufacturing a mold in a short period of time with high work efficiency.

A mold data preparation device 1 prepares mold data by computing shapes and dimensions of a plurality of molds for constructing each construction part based on data of inputted working drawing and data set about mold in advance, prepares machine tool data from the prepared mold data, and records it in the recording medium RM. A machinery controller 3 reads the machine tool data from the recording medium RM. When a machinery device 4 is set up in accordance with dimension of the mold to be machined next, a stiffener and a plate member are put on the machinery device 4 by a worker, and a start button is turned on, the machinery controller 3 controls operation of the machinery device 4 in accordance with machine tool data related to the mold to manufacture the mold.