Abstract: On the basis of NI model of ferrofluids without interaction,the relaxation of steady-field magnetization is researched by means of orientation kinetics.The numerical calculation formula of orientation distribution function and the magnetization function are obtained.Compared with the phenomenological magnetization function proposed by Shliomis,numerical calculation with advanced Galerkin method shows that the coefficient of time term is the function of magnetic field,and manifests that phenomenological formula describes the steady-field magnetization relaxation of ferrofluids as well in a certain range of field strength.