A BIM-based assembly building forward deepening design method is provided. The method comprises the following steps: determining design parameters of an assembly building according to design requirements of construction engineering, structural engineering, HVAC engineering, and electromechanical engineering, and generating an editable geometry and data information model; performing assembly component disassembling on the geometry and data information model generated in the deepening design software, and checking component parameters, so that the component size and weight meet the requirementsfor production, transportation, and installation; performing modeling on the protruding bar, the component bracing, the formwork, and the protective frame of the assembly component, and performing dynamic collision inspection on the installation of the assembly component; performing new collision inspection, and performing non-extension rib modeling of the component after there is no collision conflict; automatically generating an assembly building construction drawing and a component drawing by using a BIM drawing output module, and generating a component production material list; and finally, deriving a deeply designed BIM model to assist the mold design. According to the method provided by the present invention, the design cycle is shortened, and coordination of various professions is facilitated.