Hydrogen Decrepitation (HD) has been used as an efficient and economical method in producing coarse NdFeB powder. This article studied the effects of hydrogen on the Nd Dy Fe B magnets, such as HD powder oxidation and magnetic performance of sintered magnets. The results showed that the hydrogen accelerated the oxidation of the coarse Nd Dy Fe B powder after HD process, and the dehydrogenated powder had higher oxidation resistance, especially degassed at higher temperature, and the hydrogen dropped the sintering temperature of Nd Dy Fe B magnets. The effects of hydrogen may focus on that hydrogen bonds accelerate absorption of water from ambient air, and the defects caused by hydrogen induce oxygen diffusing more quickly. The magnets could be sintered at a lower temperature with un dehydrogenated HD powder, but had poorer orientation degree.