In the traditional RFID (Radio Frequency IDentification) system, a secure wired channel communication is used between the reader and the server. The newly produced mobile RFID system is different from the traditional RFID system, the communication between the reader and the server is based on a wireless channel, and the authentication protocol is suitable for traditional RFID systems, but it cannot be used in mobile RFID systems. To solve this problem, a mutual authentication protocol MSB (Most Significant Bit) for super lightweight mobile radio frequency identification system is proposed based on bit replacement operation. MSB is a bitwise operation to encrypt information and reduce the computational load of communication entities. Label, readers, and servers authenticate first and then communicate, MSB may be used to resistant to common attacks. The security analysis of the protocol shows that the protocol has high security properties, the performance analysis of the protocol shows that the protocol has the characteristics of low computational complexity, the formal analysis of the protocol based on GNY logic Gong et al. (1990) provides a rigorous reasoning proof process for the protocol.