The invention provides a temperature monitoring device and method for a dry air-core reactor. The device comprises multiple pairs of temperature sensors, at least one data sampling and processing module, a communication module and an upper computer. Temperature data of the upper and lower ends of air passages of coating and sealing compartments is collected by the temperature sensors and output to the data sampling and processing module; the corresponding temperature data together with sampling time node data is uploaded to the upper computer through the communication module by the data sampling and processing module; the change rate of the temperature data difference value of the upper and lower ends of the same air passage of the corresponding coating and sealing compartment is calculated by the upper computer and used as the change rate of temperature rising, failures in the initial period or the evolutionary period of generation of the dry air-core reactor are judged, and failure alerts of the initial period or the evolutionary period are raised. By means of the device and method, the failures in the initial period or the evolutionary period of the dry air-core reactor are judged, so that recognizing, monitoring and early warning of the failures in the initial period or the evolutionary period of the dry air-core reactor are achieved.