The invention discloses a preparation method of a rare earth complex crystal boundary modification sintered neodymium-iron-boron magnetic body. The preparation method comprises the following steps of: preparing neodymium-iron-boron alloy particles, smashing the neodymium-iron-boron alloy particles into powder and injecting an antioxidant; ejecting mixed liquid of a rare earth complex and petroleum into neodymium-iron-boron powder in a spraying manner and mixing uniformly; and pressing the mixture into a blank magnetic body in magnetic aligning and sintering. In the preparation method, the mixture of the rare earth complex and the petroleum is added in the spraying manner, so that contact of the particles with oxygen can be effectively prevented, the oxygen absorption in the magnetic body preparing process is lowered, and the magnetic performance of the sintered magnetic body is enhanced. The rare earth complex is added and a rare earth product left by the decomposition of the sinteredrare earth complex is mainly positioned at a crystal boundary, so that the prepared sintered neodymium-iron-boron magnetic body has a higher coercive force value and a lower temperature coefficient compared with the conventional sintered neodymium-iron-boron magnetic body. Moreover, the preparation method has a simple process, is easy to operate, and is suitable for batch production.