The invention provides a method for aligning temperature measuring holes after the assembly of an extrusion cylinder. The method comprises a step of providing an outer cylinder and an inner cylinder which are in interference fit, a step of forming an outer cylinder temperature measuring hole and an inner cylinder temperature measuring hole in the outer cylinder and the inner cylinder respectively,a step of aligning the outer cylinder temperature measuring hole and the inner cylinder temperature measuring hole in an axial direction and a circumferential direction after assembly, a step of setting an outer cylinder positioning block with an outer cylinder positioning surface on an end surface of a large end of the outer cylinder, a step of setting an inner cylinder positioning block with aninner cylinder positioning surface on an end surface of a large end of the inner cylinder, a step of heating the outer cylinder, placing the inner cylinder in the outer cylinder, and oppositely attaching the outer barrel positioning face to the inner cylinder positioning face, and a step of cooling the extrusion cylinder, wherein the cooling rates of a small end of the outer cylinder and a smallend of the inner cylinder are higher than that of other parts of the extrusion cylinder. According to the method, by setting the positioning blocks with the mutually attached positioning surfaces on the outer cylinder and the inner cylinder, the temperature measuring holes are aligned in the axial direction and the circumferential direction, by limiting the cooling condition of the extrusion cylinder after assembly, a condition that alignment of the temperature measuring holes in the axial direction does not deviate is ensured.