Abstract: This paper presents a frequency reconfigurable antenna for the Power Internet of Things targeting 5th generation mobile communication technology (5G) communication and narrow band internet of things (NB-IoT). The antenna comprises two "L"-shaped radiating branches, a ground plane with a defective structure, and a microstrip line for feeding, with PIN diodes connecting the radiating branches and the microstrip line. By adjusting the PIN diodes, the surface current distribution of the antenna can be modified, achieving excellent reconfigurability. Furthermore, by altering the defective structure, the antenna can achieve a wider bandwidth by increasing the current path. The results demonstrate that the antenna has a size of 0.43λ₀×0.49λ₀, and can operate in the NB-IoT band (1.85 GHz~1.90 GHz) and 5G communication band (4.4 GHz~5.0 GHz), with maximum gain of 4.5 dBi and 5.9 dBi, respectively. In practical applications, this antenna can be utilized in cognitive radio technology to detect idle spectrum in the 5G communication band and promptly switch to the NB-IoT operating state on idle frequencies. This allows for better meeting the requirements of deep grid monitoring and intelligent operations such as power generation and transmission.