The invention belongs to the technical field of polylactic acid micropowder, and discloses a polylactic acid micropowder prepared through high pressure homogenization assisted method, a composite material, and a method thereof. The preparation method of the polylactic acid micropowder prepared through high pressure homogenization assisted method comprises following steps: 1, polylactic acid is dissolved in a polylactic acid good solvent to obtain a polylactic acid solution; 2, a polylactic acid poor solvent is added into the obtained polylactic acid solution dropwise for precipitation of a precipitate, the precipitate is washed until pH value becomes 7 so as to obtain a primary polylactic acid micropowder; and 3, the primary polylactic acid micropowder is dispersed in a solvent for high pressure homogenization and drying so as to obtain the polylactic acid micropowder. The composite material is prepared from the polylactic acid micropowder and a laminated filling material through highpressure homogenization and moulding. The method is simple, is high in efficiency, and low in cost, and is convenient for industrialized production. The particle diameter distribution range of the prepared polylactic acid micropowder is narrow; heat performance is excellent; stability is high; the filling material dispersion in the prepared composite material is more uniform, and composite material heat conduction coefficient is increased.