RFID technology plays an important role in our daily life nowadays. It widely used in the automatic identification system by embedding the tag into product. However, some security risks presented due to radio frequency signal channel between the tag and the reader which may lead privacy disclosure for the user. Various solutions are proposed to resole to security issues in RFID system, but there still presented some limitations. A security elliptic curve cryptography based authentication protocol is presented in this paper to preserve the privacy of the RFID system. The proposed protocol provides mutual authentication and a security communication channel between the tag and the reader. By the security analysis, our protocol can resist common passive and active attack; moreover, it also can provide forward security.