The invention discloses a preparation method of a high-strength polypropylene material. The preparation method is characterized in that in the machining process, the crystal habit of polypropylene is regulated and controlled, and therefore the mechanical performance of polypropylene is improved. In the machining process, a certain shear and two-way stretch force field is applied to polypropylene melt by regulating the number and type of force assembling units, under the action of the force field, the crystal habit of polypropylene is developed into shish-kebab structures orientated in different directions, the stretch strength of the polypropylene material can be remarkably improved, and the difference of the mechanical strength, in the extrusion direction, of the polypropylene product and the mechanical strength in the direction perpendicular to the extrusion direction, of the polypropylene product is weakened. The force assembling units are added to existing traditional extrusion equipment, operation is easy, continuous production can be achieved, control is convenient, quality is stable, production efficiency is high, and good industrial and market prospects are achieved; and the method can be widely applied to preparing high-strength polypropylene plate, sheet and film materials.