Abstract: In the early stage of electrified railways, AC-DC electric locomotives served as the primary traction power. Due to the inherent drawback of low power factor in such locomotives, fixed capacitor compensation devices were commonly installed in traction substations to improve power quality and raise the power factor. With the iterative upgrading of electric locomotive technologies, AC-DC-AC electric locomotives have been extensively promoted and applied by virtue of their superior performance. In recent years, most newly constructed and put-into-operation electrified railways have adopted such AC drive locomotives. However, in some electrified railway lines where AC-DC and AC-DC-AC locomotives operate in a mixed mode, the traditional fixed capacitor power factor compensation scheme has gradually exposed defects of insufficient adaptability. Taking a traction substation equipped with fixed capacitor compensation devices as the research object, this paper conducts an in-depth analysis of its compensation effect, identifies the existing problems in the current scheme, and puts forward targeted improvement measures, aiming to provide technical reference for power factor optimization of traction substations in electrified railways under the mixed operation scenario of AC-DC and AC-DC-AC locomotives.