With the construction of high-quality distribution network stations, more and more monitoring devices are extended to the low-voltage side of the distribution network, providing new ideas for fault location on the distribution network. This paper presents a method for locating fault sections of a distribution network based on voltage changes on the secondary side of transformers in the station area. It analyzes the voltage change law on the transformer side of the distribution network after a fault occurs, and uses the difference between the three-phase voltage amplitude changes at the monitoring point under the fault path and the non-fault path to identify the faulty section. It uses an improved nearest neighbor clustering method to identify the set of monitoring points at different locations from the fault in the voltage monitoring set. This can quickly partition the monitoring information. This method does not require 10 kV line monitoring data, but only needs 10/0.4 kV transformer low-voltage side voltage amplitude change information in the distribution station area. The monitoring collection device is easy to install and maintain. A large number of simulations show that the method can adapt to different neutral grounding methods, fault types and transition resistances, and has strong applicability. This work is supported by the National Key Research and Development Program of China (No. 2020YFF0305800).