Abstract: Electric propulsion technology is an important technical approach to unknown fields of space with knowledge growing of outer spaceenvironment. The different effects, spacecraft protective structure, energy system, payload system are sensitive to space electric propulsion system. The Retarding Potential Analyzer detecting method of Electric Propulsion is described. The Retarding Potential Analyzer is researched and manufactured. The ground simulation experiments about Retarding Potential Analyzer showed the nozzle of thruster 40 cm particle energy, ion density and ion temperature. The technical reference for electric propulsion spacecraft application and development in deep Space are provided.