Ni-coating is usually adopted to protect the sintered NdFeB magnet by electrodeposition.But the poor adhesion strength between Ni-coating and NdFeB substrate can’t satisfy the requirement in some engineer fields especially on magnetoelectric machine.In order to study the influence factors to adhesion strength in the processes of pretreatment,the derusting process of NdFeB in nitric acid solution was studied.Through the component analysis of NdFeB,it was found that NdFeB comprise three phases (the main phase Nd2Fe14B,Nd-rich and B-rich),and the Nd-rich and B-rich localize in the grain boundary of Nd2Fe14B.In order to research the corrosion behavior of three pure phases mentioned above,they were prepared by arc melting method,and the electrochemistry station was used to measure the corrosion behavior of three pure phases,Through the analysis of EIS,ECN and polarization curve,it was concluded that the Nd-rich erode faster than other two composing phases,which result in loose structure in the surface layer of NdFeB subtrate,then the reduction of adhesion strength during Ni electrodepositing on NdFeB substrate.