The state of NdFeB powder, especially the particle size distribution and particle shape have an important influence on the orientation degree of the magnet and the sintering process. The traditional methods of powder preparation are mechanical crushing and ball milling. Mechanical crushing is carried out under the protection of inert gas by jaw crushing, ball milling with sieve and other methods. Ball milling includes vibrating ball milling and rolling ball milling, etc. The powder prepared by vibrating ball milling is irregular in shape, which is not conducive to magnetic field orientation; rolling ball milling requires gasoline protection, the process is complex and the efficiency is not high. At present, NdFeB manufacturers basically use jet mill to make powder. Jet mill powder is pulverized by the high-speed collision of the material itself, which has no wear and pollution to the inner wall of the mill, and can prepare powder with high efficiency. However, this process seriously damages the grain structure of the main phase of the alloy, so that the neodymium-rich phase cannot be uniformly distributed on the grain boundary of the main phase, especially for some alloys with coarse grains, the broken main phase grains and the neodymium-rich phase are respectively separation, it is impossible to prepare high-performance magnets. Now the HD process is adopted, that is, the NdFeB alloy is placed in a hydrogen environment, and the hydrogen enters the alloy along the Nd-rich phase thin layer, causing it to expand, burst and break, and crack along the Nd-rich phase layer to ensure the main phase grain and Nd-rich phase. The integrity of the grain boundary phase. The powder prepared by the jet mill after being crushed by the HD process has a concentrated particle size distribution and few surface defects, which can be used to manufacture high-performance magnets. Rare earth elements are very easy to be oxidized. Because the particle size of NdFeB powder is particularly small, it is easy to oxidize. Therefore, inert gas protection should be used during the process of jet milling. At the same time, adding a certain proportion of antioxidants before milling can protect the powder. It is not easy to be oxidized and can improve the milling efficiency.