Abstract: A four-grid Retarding Potential Analyzer （RPA） with size of Φ19 mm×24 mm was designed and developed in order to enhance the measurement resolution of ion energy in electric propulsion plume. The designed critical parameters include that the grid aperture diameter was 0.3 mm, and the center distance between holes was 0.5mm,and the spacing between electron repelling grid and ion retarding grid was 2 mm, and the ion energy resolution was 9.8%.The results validated in plume of the LIPS-200 ion electric propulsion for RPA show that the ion energy was distributed from 955 eV to 1047 eV, and the average ion energy was 1001.0 eV, and the ΔE_FWHM was 36.1 eV, and the ion energy resolution was 3.6%. The results validated in plume of the LHT-40 Hall electric propulsion for RPA show that the ion energy was distributed from 220 eV to 279 eV, and the average ion energy was 249.6.0 eV, and the ΔE_FWHM was 23.4 eV, and the ion energy resolution was 9.4%.The ion energy resolution of RPA with less uncertainty is superior to that of the similar product at home and abroad.