The levels HL1～HL5 of a hierarchical model for the reliability evaluation of the traction power supply system of a high-speed railway is proposed. For level HL1， the reliability evaluation model of the bulk power system for the traction power supply system has been developed with the section-crossing supply between substations taken into account. The analytical expressions of the reliability indices and sensitivity to the system component reliability parameters have been deduced. Hence the power supply reliabilities of all the traction power supply substations and the carrying capacity of the high-speed railway have been evaluated. The reliability evaluation and sensitivity analysis have been made on the IEEE RTS79 power system which provides power to a high-speed railway line， with the weak links determined.