Abstract: The deep coupling between the network layer and the physical layer of the power system increases the risk of cyber attacks. The automatic generation control（AGC） system is one of the few closed-loop control system in the power system with less human intervention. It plays an important role in maintaining the balance of active power and the stability of frequency in power systems. Existing studies show that cyber-attacks can deteriorate the control effect of AGC and even cause collapse of the power system. Consequently, the cyber attack against AGC has attracted widespread attention in various fields. In view of this, this paper summarizes the research status of cyber attacks against the AGC system from the perspective of attack forms, attack variables,attack detection and defense. The typical cyber attacks and defense cases are analyzed, and the countermeasures against cyber attacks on the AGC system are discussed. Finally, the future research directions of defense against cyber attack and defense of the AGC system are prospected.