In order to understand the adhesion failure between Ni-coating and sintered NdFeB substrate, the effect of pickling process on the adhesion strength of Ni-coating on NdFeB substrate was studied. The results reveal that the pickling leads to the formation of loose structure on NdFeB surface and the reduction of micro-hardness of NdFeB surface. The adhesion strength of Ni-coating on NdFeB substrate declines gradually with the increasing time of pickling. It can be found from the cross section morphology of stripped layer that the adhesion failure occurs in inner NdFeB substrate close to the surface, rather than in the interface between Ni-coating and NdFeB substrate.