The invention discloses a method for preparing anisotropic neodymium iron boron magnetic powder through directionally breaking a thermal deformed magnet. The method comprises the following steps: (1) preparing a full-densification isotropic neodymium iron boron magnet; (2) preparing a thermal deformation anisotropic neodymium iron boron magnet; (3) directionally breaking the thermal deformation magnet: directionally breaking the round-cake-shaped anisotropic neodymium iron boron magnet, prepared in the step (2), by applying a symmetrical and circulating applied force along a radial direction at room temperature under the protection of argon, wherein the breaking force is 600-700MPa, so as to obtain a lamellar magnetic sheet; and (4) breaking the magnetic sheet in a regularized way: carrying out regularized breaking on the magnetic sheet prepared in the step (3) under the protection of the argon by adopting a rolling minding method, so as to obtain the anisotropic neodymium iron boron magnetic powder.