The invention discloses a preparation method for a polylactic acid nanofiber scaffold functionally modified by two-dimensional nanometer black phosphorus, and aim to provide a preparation method for amultifunctional modified polylactic acid scaffold. The preparation method is characterized in that a black phosphorus nanosheet is taken as a medicine carrier to load an anti-inflammatory medicine, i.e., ibuprofen, a natural high polymer material, i.e., sodium alginate, is taken as a coating material, and through a crosslinking function of strontium ions, a medicine-carrying microsphere is obtained; an electrostatic interaction is used for evenly doping a sodium alginate medicine-carrying microsphere into a modified polylactic acid basis material which is subjected to ammonolysis and modification by branched polyethyleneimine and is rich in an active amino group; and through freezing phase separation, the modified polylactic acid scaffold with a reticular nanometer fiber structure is obtained. The preparation method has the characteristics that the prepared modified polylactic acid nanofiber scaffold embedded with the medicine-carrying microsphere is a multifunctional system with thefunctions of performing photothermal therapy, accelerating bone growth, resisting bacteria, diminishing inflammation and intelligently releasing medicines, and the polylactic acid nanofiber scaffold is an ideal bone repairing material.