Fail safe improving method of HEV

The present invention relates to a fail-safe improving method of a hybrid vehicle and, more specifically, to a fail-safe improving method of a hybrid vehicle, capable of improving fail-safe by providing a stable power source to a high voltage component, which functions normally, including a high voltage electronic oil pump when a high voltage main relay is off and malfunctioned. The present invention is to improve the fail-safe of the hybrid vehicle in which the high voltage electronic oil pump is adopted and provides the fail-safe improving method of the hybrid vehicle which is characterized by increasing voltages of a power source of a low voltage battery by operating a bidirectional converter in a boost mode if an engine can be started and the voltage of the low voltage battery is over a standard voltage when the high voltage main relay is off.