Aiming at the characteristic that the existing steel structure material preparation basically relies on manual processing, the invention jumps out of the existing thinking, and puts forward a steel structure material preparation method based on a BIM system and CAD software, models the whole project by using the BIM system, and outputs CAD files of each part; CAD file is transformed by CAD secondary development plug-in a to form a program cutting diagram with part information; the CAD secondary development plug-in b is used to operate the part process cutting drawing, so that the part rotatesaccording to the smallest rectangle including its shape, and prompts to manually input the process reserved quantity, and draws the part process cutting drawing outer frame according to the input quantity, which is used as the material outline of the part; The character module is extracted by CAD secondary development plug-in c and exported to spreadsheet to form a material preparation list with complete steel plate information. Manual operation is greatly reduced, manpower consumption is reduced, and the working efficiency of material preparation is improved.