Due to its special electromagnetic characteristics, transformers may have various hidden faults that fail to trigger related protection during operation, which will endanger the safe and stable operation of equipment and power grid. This paper proposes a model based on J-A hysteresis. The method of monitoring the online operation status of the transformer is to assist the operation and maintenance personnel to judge various faults that may occur in the actual operation of the transformer. Based on this, this paper firstly establishes a transformer model based on J-A hysteresis theory, and then collects the relevant waveform acquisition of the transformer in actual operation, and uses wavelet transform to analyze the waveform of the transformer under real-time conditions and the error of the predicted waveform of the transformer model established. Verification, through the verification results to determine whether the transformer is working properly, and finally, through the simulation experiments, the reliability of the proposed monitoring method is verified.