An asymmetric extrusion method for extruding an extruding material to a plate shape, the method comprising: charging an extruding material into a container; compressing the extruding material in the container using a stem; pushing the extruding material through a die combined with an end portion of the container, and comprising an extrusion hole having a rectangular shape for extruding the extruding material to said plate shape; wherein the container includes an internal hole and the internal hole includes a first inner wall parallel to the extrusion direction, and a second inner wall parallel to and facing the first inner wall; wherein the extrusion hole of the die comprises a tapered part having a width varied according to the extrusion direction, and a fixed part having a fixed width, the tapered part having an asymmetric shape with respect to the extrusion direction of the extruding material, so as to extrude the extruding material while introducing shear strain in the extruded material; and wherein the tapered part includes a pair of first inner surfaces (142,144) and the distance between the pair of first inner surfaces (142,144) decreases along the extrusion direction of the extruding material; characterised in that: a first surface of the pair of first inner surfaces is connected to the first inner wall, on the same plane with the first inner wall and parallel to the extrusion direction of the extruding material; and a second surface of the pair of first inner surfaces is connected to the second inner wall, faces the first surface of the pair of first inner surfaces and is inclined to the extrusion direction of the extruding material. charging an extruding material into a container; compressing the extruding material in the container using a stem; pushing the extruding material through a die combined with an end portion of the container, and comprising an extrusion hole having a rectangular shape for extruding the extruding material to said plate shape; wherein the container includes an internal hole and the internal hole includes a first inner wall parallel to the extrusion direction, and a second inner wall parallel to and facing the first inner wall; wherein the extrusion hole of the die comprises a tapered part having a width varied according to the extrusion direction, and a fixed part having a fixed width, the tapered part having an asymmetric shape with respect to the extrusion direction of the extruding material, so as to extrude the extruding material while introducing shear strain in the extruded material; and wherein the tapered part includes a pair of first inner surfaces (142,144) and the distance between the pair of first inner surfaces (142,144) decreases along the extrusion direction of the extruding material; characterised in that: a first surface of the pair of first inner surfaces is connected to the first inner wall, on the same plane with the first inner wall and parallel to the extrusion direction of the extruding material; and a second surface of the pair of first inner surfaces is connected to the second inner wall, faces the first surface of the pair of first inner surfaces and is inclined to the extrusion direction of the extruding material. a first surface of the pair of first inner surfaces is connected to the first inner wall, on the same plane with the first inner wall and parallel to the extrusion direction of the extruding material; and a second surface of the pair of first inner surfaces is connected to the second inner wall, faces the first surface of the pair of first inner surfaces and is inclined to the extrusion direction of the extruding material.