The power supply maintenance of sensors will hinder the application and development of the IoT (internet of things) system in substations. To handle it, this paper proposes a new power supply method for the IoT system in substations based on the wireless transmission to realize itsself-sustaining operations. Firstly, the energy acquisition and distribution model is established, the signal transmission model is analyzed, and the CSMA protocol is used to transmit signals on the time-slot shared channel to communicate with the power supply nodes, which can effectively reduce the multi-node wireless power supply channel competition. Secondly, the evolution of sensor energy is analyzed, and two sensor energy supply schemes are designed. Among them, the sub-optimal scheme assigns power to each node fixedly to achieve simpler implementation rather than performance.The other scheme will dynamically adjust the allocation, to provide the maximum power for each node, and get the best energy distribution ratio which can improve the wireless power supply efficiency of the system. Finally, a 10-node simulation model is established to verify the effectiveness of the proposed method. The results show that the method proposed in this paper can realize the self-sustaining of the substation IoT system.