Abstract: The step motion of control rod drive mechanism is accomplished through the lift armature of claw assembly hoisting and falling alternation movement in the vertical direction. In the base of the control rod drive mechanism step motion decomposition, the dynamic calculation model of coupled magnetic-electric-mechanical movement is established by finite element calculation method. The relations between magnetic force, electric current, displacement and time are studied in the process of control rod drive mechanism stepping motion. The movement characteristic parameters as hoisting time, falling time, electric current and magnetic force are obtained. The results can be applied to the time sequence design of control rod drive mechanism.