A mechanical pulverizer adopts multi-stage high-speed rotating turbine and special design structure to achieve ultrafine or nano pulverization. As shown in the figures, the mechanical pulverizer comprises: base plate (1), bearing seats (2 and 3), main shaft (4), motor base (5), main motor (6), casing (7 and 7′), three-stage turbine blisks (8, 9 and 10), multi-surface curved turbine blades (11 and 11′), gear rings with large-angle curved gears (12 and 12′), suspended shearing device (13 and 13′), built-in, unpowered and replaceable grading plates, (14 and 15), feeding inlets (16 and 17), spiral feeder (18), discharge outlet (19), residuals outlet (20), nanometer filter cloth material collecting bin (21), screw rod for casing-opening (22), handle for casing-opening (23), self-pressurized automatic-control liquid nitrogen cooling device (24), and liquid nitrogen conveying pipes (25).