To establish green power systems, the development of clean but uncertain renewables has drawn global attention. Meanwhile, controllable resources with high carbon emissions such as coal-fired units (CFUs) are gradually degrading. Under this circumstance, it is a severe challenge for the automatic generation control (AGC) system to maintain the frequency performance of power systems. To solve this, it is necessary to make full use of the regulation capacity of different types of regulation resources in AGC command allocation. Among the resources, gas turbine units (GTUs) have a special operating area named the temperature control area (TCA). When operating in the TCA, the regulating capability of GTUs will greatly decrease, which affects the system frequency performance. Moreover, the safety of GTUs will also be affected. With this in mind, an AGC command allocation method considering the TCA of GTUs is proposed in this paper. Firstly, the characteristics of GTUs are analyzed. Then, the AGC command allocation method considering multi-type regulation resources including GTUs, CFUs, hydropower units (HPUs), and energy storage systems (ESSs) is proposed. Allocating priorities are designed for different types of regulation resources to coordinate their discrepant characteristics. Besides, priorities will be adjusted according to whether GTUs are operating in the TCA, aiming to prevent GTUs from operating in the TCA for a long time. Finally, time-domine simulations are conducted based on practical data to demonstrate the effectiveness of the proposed method.