The research object of this paper is the factory test scheme for factory test of step-by-step control valve control logic in nuclear power plant safety DCS. The step-by-step control valves are widely used in the field process control of nuclear power plants. DCS outputs pulse signals of different frequencies and widths through the logic of step-by-step control valve to drive stepping motors to realize the control function. In this paper, the design process of the control logic of the step-by-step control valve is analyzed from top to bottom, combined with the requirements of DCS test standard for nuclear power plants, a bottom to up test strategy for the control logic of safety DCS step-by-step control valve in nuclear power plants is proposed, aiming at the strict timing requirements of the control logic of step-by-step control valve, the coverage principle of step-by-step control valve control logic and the test scheme of standardized output waveform are proposed to ensure the integrity, effectiveness and quality of DCS step-by-step control valve control system.