Abstract: As the proportion of power electronic devices rises, the transient frequency issue in power systems is increasingly conspicuous. Aiming at the current problems of unclear determination conditions of transient frequency security and unclear control methods to ensure transient frequency security under low inertia conditions, this paper comprehends the transient frequency issue, clarifies the essence of transient frequency issue, gives the conditions of transient frequency security determination from the perspective of energy, and initially explores the control methods of transient frequency security from an energy viewpoint. Firstly, this paper retraces the historical development, essence, and primary constraints of transient frequency issues while discussing their evolution. It dissects the sources of energy and response forms in inertia and primary frequency control, analyzing their relationship and interactions from an energy perspective and establishing critical conditions for transient frequency security from an energy perspective. Finally, inertial energy and primary frequency regulation energy from the energy perspective are discussed, and the optimal strategy of primary frequency regulation energy is initially investigated, giving a transient frequency control idea.