The invention provides a transformer region low-voltage cause analysis method and system. The method comprises the following steps: to begin with, according to collected transformer region network parameters and collected transformer region operation parameters, establishing transformer region network topology and component models thereof; then, calculating a transformer region low-voltage quantitative evaluation index--low-voltage index under the current state through load flow calculation; on the basis of the current state of the transformer region, through a variable parameter method, adjusting various factors closely related to the low voltage gradually till the corresponding indexes return to normal, and calculating transformer region low-voltage indexes when adjusting various factorstill the corresponding indexes return to normal respectively; and calculating the difference values between the transformer region low-voltage indexes obtained when adjusting the various factors tillthe corresponding indexes return to normal and the low-voltage index obtained in the step 4), and comparing the difference values, the smaller the difference value being, the higher the dependency between the factors and the low voltage being, and thus main cause of the transformer region low voltage can be obtained. The method is simple and high in operability, and can provide targeted decisionbasis for low-voltage treatment.