A high-reliability multiphase power supply system and method. A second processing unit is configured with a first field-effect transistor, a drain electrode of the first field-effect transistor is connected to a power supply, a source electrode of the first field-effect transistor is connected to the drain electrode of a second field-effect transistor, the source electrode of the second field-effect transistor is connected to ground, and the gate electrodes of the first field-effect transistor and the second field-effect transistor are connected to a first processing unit; the second processing unit is configured with a first current detection module and a second current detection module, the first current detection module and the second current detection module are electrically connected to a bus unit, and the bus unit is electrically connected to a substrate management controller.