The invention belongs to the technical field of cable facilities in transformer substations, and particularly relates to a prefabricated finished cable trench. The prefabricated finished cable trench comprises a plurality of cable trench bodies and cable holders in the cable trench bodies. Each cable trench body comprises a first base plate and a second base plate which are connected fixedly. First trench walls and first square steel sets are arranged on the upper end faces of the first base plates from left to right. First cover plates are arranged at the upper ends of the first trench walls and the first square steel sets. Second square steel sets and second trench walls are arranged on the upper end faces of the second base plates. Second cover plates are arranged at the upper ends of the second squire steel sets and the second trench walls. The prefabricated finished cable trench has the advantages that the longitudinal depth design of conventional cable trenches is changed into flattening design, so that on the premise of guaranteeing utilization rate of cable channel sections, construction difficulty in laying of cables is reduced, and convenience is brought to follow-up maintenance and operation; multiple prefabricated modules are matched flexibly to splice cable trenches with different widths, and the prefabricated finished cable trench is applicable to cable laying at different places.