A method of preparing a sintered NdFeB magnet, said method comprising the steps of: a) pressing magnetic powders into a green compact under a magnetic field and then demagnetization; b) isostatic pressing the green compact; c) fixing the green compact on a special device comprising: a reciprocating cutting mechanism, a cutting tooling, a green compact fixed tooling and a reciprocating lifting mechanism, wherein the reciprocating cutting mechanism is connected to the cutting tooling, the reciprocating lifting mechanism is connected to the green compact fixed tooling, the reciprocating cutting mechanism is adapted for reciprocating in a horizontal direction, and the reciprocating lifting mechanism is adapted for realizing a reciprocating lifting in a vertical direction; the green compact fixed tooling comprises a pair of trunking plates, a pair of limit guiding plates, guiding pins, adjusting bolts and a base, wherein the pair of trunking plates is mounted on opposite sides of the base, the pair of limit guiding plates is mounted to the end of the trunking plates, and the limit guiding plates are provided with the guiding pins and adjusting bolts; and the cutting tooling comprises a pair of wire fixing boards, cutting wires, adjusting screws, and a fixing plate, wherein the pair of wire fixing boards is mounted on the fixing plate and the cutting wires are tensioned by means of the adjusting screws between the the pair of wire fixing boards, and then machining the green compact into a finished shape and corresponding size on one or two surfaces among an orientation surface, non-orientation surface and pressing surface; d) sintering and annealing the machined green compact; and e) machining the obtained blank into a finished product. a) pressing magnetic powders into a green compact under a magnetic field and then demagnetization; b) isostatic pressing the green compact; c) fixing the green compact on a special device comprising: a reciprocating cutting mechanism, a cutting tooling, a green compact fixed tooling and a reciprocating lifting mechanism, wherein the reciprocating cutting mechanism is connected to the cutting tooling, the reciprocating lifting mechanism is connected to the green compact fixed tooling, the reciprocating cutting mechanism is adapted for reciprocating in a horizontal direction, and the reciprocating lifting mechanism is adapted for realizing a reciprocating lifting in a vertical direction; the green compact fixed tooling comprises a pair of trunking plates, a pair of limit guiding plates, guiding pins, adjusting bolts and a base, wherein the pair of trunking plates is mounted on opposite sides of the base, the pair of limit guiding plates is mounted to the end of the trunking plates, and the limit guiding plates are provided with the guiding pins and adjusting bolts; and the cutting tooling comprises a pair of wire fixing boards, cutting wires, adjusting screws, and a fixing plate, wherein the pair of wire fixing boards is mounted on the fixing plate and the cutting wires are tensioned by means of the adjusting screws between the the pair of wire fixing boards, and then machining the green compact into a finished shape and corresponding size on one or two surfaces among an orientation surface, non-orientation surface and pressing surface; a reciprocating cutting mechanism, a cutting tooling, a green compact fixed tooling and a reciprocating lifting mechanism, wherein the reciprocating cutting mechanism is connected to the cutting tooling, the reciprocating lifting mechanism is connected to the green compact fixed tooling, the reciprocating cutting mechanism is adapted for reciprocating in a horizontal direction, and the reciprocating lifting mechanism is adapted for realizing a reciprocating lifting in a vertical direction; the green compact fixed tooling comprises a pair of trunking plates, a pair of limit guiding plates, guiding pins, adjusting bolts and a base, wherein the pair of trunking plates is mounted on opposite sides of the base, the pair of limit guiding plates is mounted to the end of the trunking plates, and the limit guiding plates are provided with the guiding pins and adjusting bolts; and the cutting tooling comprises a pair of wire fixing boards, cutting wires, adjusting screws, and a fixing plate, wherein the pair of wire fixing boards is mounted on the fixing plate and the cutting wires are tensioned by means of the adjusting screws between the the pair of wire fixing boards, and then machining the green compact into a finished shape and corresponding size on one or two surfaces among an orientation surface, non-orientation surface and pressing surface; d) sintering and annealing the machined green compact; and e) machining the obtained blank into a finished product.