Abstract: Direct current (DC) ionized field generator plays an important role in the test and calibration of electric field sensors under the condition of ionized field. Traditional DC ionized field generator is difficult to meet the development needs of novel electric field sensors and inconvenient to apply in outdoor fields for its large volume. This paper presents a reduced-scale DC ionized field generator. Based on theoretical calculations and finite element simulation, the critical parameters of device size and structure are analyzed and optimized. The structure is optimized and the fringing field effect is eliminated by equaling potential at the edge of the parallel plate. So the uniform electric field region between the parallel plates is increased and the uniformity error of electric field is reduced. The experimental results show that the relative average deviation of the ion current intensity at different places of the ionized field is only 1.66% when the voltage of corona wires is 7 kV. The reduced-scale DC ionized field generator presented in this paper can generate the uniform ionized field.