Since the computational complexity of public key cryptography is high, and Power Delay Profile (PDP) model is limited by the distance between the attacker and the user, a wireless communication security strategy based on Differential Flag Byte (DFB) was proposed in the identification and defense of impersonation attack. Meanwhile, the equation to generate the DFB was given. The strategy utilized the transmission data information to generate the DFB equation, establishing the correlation that current flag byte of transmission data frame was determined by the relevant parameter of last frame. Finally, receiving terminal identified attack by testing and verifying the DFB received from the data frame with threshold decision. Through theoretical analysis, DFB could prevent recurrent impersonation attack, when the attacker knew the communicational parameter. Meanwhile, the attacker's effective attack time was shorter, and the attack cycle was longer. And the attacker was limited to a finite ellipse in space. Simulation analysis was carried out with a simple DFB at the end. The results show that wireless communication based on the simple DFB strategy can identify and defense impersonation attack by setting the appropriate threshold, when the communication system's Signal-to-Noise Ratio (SNR) was above -4 dB.