To ensure the safe and reliable operation of distribution transformer, an automatic capacity verification method based on data clustering is proposed. By improving the fuzzy C-means clustering algorithm, the membership degree between each data sample and all clusters is calculated, and the historical voltage drop data of the distribution transformer is clustered; Based on the load factor and voltage change rate of the transformer, the capacity of the distribution transformer is automatically checked by the time difference method. The test results show that the method can effectively complete the voltage drop data clustering of the transformer, and the Xie-Beni coefficient calculation results are all below 0.030. It can greatly reduce the influence of noise data on the transformer capacity check, and reliably complete the automatic check of the transformer capacity. The average root mean square error of the check results is above 0.89.