Abstract: Compared with the traditional unilateral power supply system, the electrical structure of the bilateral power supply system of electrified railway has changed, resulting in the unclear voltage level of the external power supply side and the traction power supply system side, which is not conducive to the scheme design and optimization in practical engineering. Therefore, a voltage level analysis system based on three-phase voltage deviation, three-phase voltage unbalance and catenary network voltage level is constructed, and the power flow calculation method of traction power supply system is used to analyze the system power flow. On this basis, the variation law of the system voltage level is explored, and the key factors affecting the system voltage level are clarified based on the sensitivity analysis method. The results show that the catenary voltage level of the bilateral power supply system is higher than that of the unilateral power supply system, and the voltage level at the common connection point is related to the external power supply mode of the unilateral power supply system. The choice of a three-phase-to-two-phase transformer as the interface between the traction power supply system and the external power supply, or the corresponding measures to reduce the equivalent impedance from the power point to the load, can help to increase the system voltage level. Increasing the short-circuit capacity of an external power supply is the most effective way to increase the voltage level at the common connection point.