The invention provides a coaxial cable power supply system of an electrified railway. The coaxial cable power supply system is composed of a center traction substation, coaxial cables, traction transformers, a contact system, a steel rail, circuit breakers and the like, wherein the center traction substation is connected with the coaxial cables; the coaxial cables are erected parallel with the contact system; the traction transformers are in single-phase connection, and are distributed along the coaxial cables and the contact system at certain intervals; a primary winding of each traction transformer is connected between an inner conductor and an outer conductor of the corresponding coaxial cable in parallel; a secondary winding of each traction transformer is connected between the contact system and the steel rail in parallel; the inner conductors of the coaxial cables are connected in parallel with the contact system by the adjacent traction transformers; the outer conductors of the coaxial cables are connected in parallel with the steel rail by the adjacent traction transformers. According to the coaxial cable power supply system, the power supply capacity and the voltage level are mainly determined by the coaxial cables; therefore the system is applicable for matching between the coaxial cables and various voltage grades of the contact system, and is beneficial to improving the light suspension and the overall quality of the contact system; the coaxial cables are erected along a railway or a subway tunnel without occupying additional corridors, so that interfaces between the railway and the public power grid can be reduced, the external power investment can be saved, and the management is facilitated.