In order to improve the longitudinal uniformity of temperature distribution and the threshold power of stimulated Brillouin scattering effect of rare earth doped fiber，the preparation method of rare earth doped fiber with gradient distribution of rare earth ion doping concentration along the longitudinal distance of the fiber is studied.The relationship between the technological requirements of the preparation of rare earth doped graded preform and the geometrical size of the optical fiber is analyzed.Based on the method of ionic liquid phase doping,using the technology of porous layer division and multiple immersion,ytterbium ion achieved gradient doping with four steps in the length range of 28.0 mm in the fiber preform.The 976 nm cladding absorption coefficient of 11.2 m graded doped fiber is measured after the graded doped preform is drawn into the rare earth doped fiber.The absorption coefficient in the high doping concentration region is 2.57 times of that in the low doping concentration region.