This paper presented basic functions and work principles of d.c. charging system for Electric Vehicle in international standard IEC 61851-23. A verification method of key parameters for compatibility and security of the charging process between off-board charger and electric vehicle was designed. Based on the constructed test system, different charging stage and timing tests, communication protocol test, charging control performance test, charging fault protection test were realized. Testing results showed that the proposed method could be made the comprehensive verification and analysis on the key performance index within international standard of off-board charger. It would conducive to future standardization and internationalization of China"s electric vehicle charging products.