Radio　Frequency　Identification　(RFID)　technologies　have　been　standardized　and　commercialized,　but　privacy　problem　is　a　major　challenge　due　to　no　ideal　solution　used　in　RFID　system.　We　propose　an　efficient　authentication　protocol　conforming　to　the　EPCglobal　standard　for　RFID　security　system　to　solve　the　privacy　problem　such　as　tracing　and　eavesdropping.　Firstly　we　provide　a　comprehensive　discussion　of　privacy　problems　and　current　technologies.　secondly　we　illustrate　the　structure　of　protocol.　Thirdly　we　describe　how　the　mutual　authentication　and　encrypted　communication　are　executed　between　a　tag　and　a　reader.　Finally　the　security　analysis　on　withstanding　attackers　for　RFID　system　is　given.　The　security　analysis　results　show　that　the　proposed　protocol　is　feasible　in　RFID　security　system.