The invention discloses a method for fault diagnosis of a transformer substation. The method comprises the steps of constructing a first fuzzy rule matrix according to the causal relationship of different association nodes of the transformer substation, wherein each association node comprises a relay, a breaker and a preset fault area, and the element of the first fuzzy rule matrix comprises preset causal relationship values between the association nodes; constructing a first state vector according to obtained first state information of the relays and the breakers in the fault process of the transformer substation, wherein the element of the first state vector comprises first state values corresponding to the association nodes; conducting blurring operation on the first fuzzy rule matrix and the first state vector, updating the first state value in the first state vector according to the preset causal relationship values, and obtaining a second state value; comparing the second state value corresponding to a preset fault area with the fault threshold value, and determining the target fault area in the preset fault area. According to the method, the accuracy and rate of fault diagnosis of the transformer substation are improved.