The invention provides a bottom layer optimization method for a digital model under a tractive power supply system BS frame. The method includes the specific steps that entities needing to be digitally established are analyzed, the entities are classified according to majors, classes, units and the like, and finally minimum units capable of being recombined of the entities are calculated; a simulation model is established through 3dmax and is normatively named; in a unity3d engine, the minimum units serve as minimum assemblies and are grouped and stored, former layer units are spliced according to the entities, splicing is sequentially conducted until the highest layer units are spliced, and then a whole digital scene can be modeled. According to the method, in final virtual simulation, only a basic model needs to be transferred through a network, programs of other whole parts are recombined according to the classes of the units and the like, and simulation efficiency of complex scenes is greatly improved.