The invention relates to an SF6 breaker state monitoring method and a thionyl fluoride gas concentration monitoring device, wherein the method is used for detecting the concentration of thionyl fluoride which is the decomposer of SF6 in an SF6 breaker, and the state of the SF6 breaker is judged by the concentration of the thionyl fluoride. The monitoring device which implements the above method comprises an information acquisition and processing unit and a processing unit, wherein the information acquisition and processing unit comprises a sensor module, a current-to-voltage conversion module and an analog-to-digital conversion module are connected in sequence, the processing unit is a controller, and the output end of the analog-to-digital conversion module is connected with the input end of the controller. The gas concentration monitoring device provided by the invention has the advantages of small size, low cost and lower cost especially in mass production and is easy to carry. The device also can well and easily detect the gas concentration, is suitable for practical engineering application, and has high detection accuracy, wide detection range and good electromagnetic disturbance resistance.