The invention discloses a ring main unit temperature and humidity evaluating device, method and system. Electric device temperature data, environment temperature data and environment humidity data in a single ring main unit transmitted by each ring main unit monitoring unit, weights of evaluation indexes of the electric device and the environment in the single ring main unit and the evaluation grade section of the temperature and the humidity of the single ring main unit are utilized to obtain an operation state evaluation result of the single ring main unit; then the temperature and humidity evaluation result of the single ring main unit, the weights of the evaluation indexes in the temperature and the humidity of the single ring main unit and the temperature and humidity evaluation grade section of a ring main unit system are utilized to obtain an operation state evaluation result of the ring main unit system. Therefore, the device, method and system solves the problem that the operation state of the single ring main unit and the whole ring main unit system under some certain temperature and humidity cannot be obtained.