In order to realize the safe and stable operation of the power grid, it is necessary to monitor the reactor in operation reasonably. In order to put forward the layout scheme of wireless temperature sensor in the on-line temperature monitoring system of dry-type air-core reactor, the finite element temperature simulation calculation is carried out according to the principle of multi-physical field coupling, and the radial and axial temperature distribution laws of the reactor are summarized and analyzed. In the radial direction, the encapsulation temperature of the middle layer was higher than that of the outer layer. In the axial direction, the temperature gradually increases from the bottom to the top, and the highest hot spot of each layer is located at the upper part of the axial height of the reactor. The accuracy of the finite element simulation calculation was confirmed by the outermost encapsulation temperature of the infrared detection, and the layout scheme of the wireless temperature sensor was proposed. The simulation is carried out when different encapsulations fail. When the reactor fails, the hottest spot of temperature changes from the top of the reactor to the fault location. The closer to the fault location, the higher the temperature rises. And the fault occurs at any position in the axial direction, at least one sensor can detect the temperature change. Combined with the distribution of hot spots in normal operation and fault, the layout position of temperature sensor is verified to improve the effectiveness and reliability of temperature detection.