The invention discloses a cable trench for a prefabricated transformer substation. The cable trench comprises a body, and an arc barrier is arranged in the body. The inner cavity of the body is divided into a first groove body and a second groove body by the arc barrier; the first groove body is corresponding to a high-voltage cabinet of the prefabricated transformer substation; the second groovebody is corresponding to a low-voltage cabinet of the prefabricated transformer substation. When arcing occurs in a gas tank or a cable chamber in a high-voltage cabinet, the arc light and pressure instantly rush into the first groove body of the cable trench and then enter the second groove body after passing through the arc barrier, and the arc light and the pressure can be effectively preventedfrom being released to a low-voltage side of a box-type transformer substation through the arc barrier, thereby effectively reducing the recoil pressure borne by the low-voltage cabinet, and guaranteeing the safety of operators on the low-voltage side.