We present a three‐dimensional code (storm‐time evolution of electron radiation belt, STEERB) for the storm‐time evolution of electron radiation belt following the preceding work. STEERB code is based on the solution of three‐dimensional modified Fokker‐Planck equation, which covers the inner and outer radiation belts with incorporation of the Coulomb collisions, radial diffusion due to magnetic and electric field perturbations, and local pitch angle, energy, and cross‐pitch angle‐energy diffusion due to various wave‐particle interactions. It is implemented by a split operator technique, in conjunction with the recently developed hybrid finite difference method for local wave‐particle interaction, and the fully implicit finite difference method for radial diffusion as well as Coulomb collisions. The resulting numerical model is robust, efficient, and easily parallelizable. Some of the dominant characteristics of electron radiation belt during both quiet and active periods can be well reproduced by STEERB code. Test simulations are performed to evaluate the respective roles of radial diffusion, cyclotron resonant interaction with chorus and plume waves in the global radiation belt dynamics, the sensitivity of numerical results to the uncertainty of wave spectrum, and the importance of cross‐pitch angle‐energy diffusion in the three‐dimensional simulations.