1. A POST (power-On-Self-Test) debugging method, executed by a processing unit, comprising: setting a phase number indicative of a current POST phase; selecting a driver from a scheduled queue; obtaining a GUID (Globally Unique Identifier) of the driver; storing or outputting the phase number and the GUID so as to recognize the driver of the phase being interrupted upon a break point of the driver; and executing the driver, wherein the step of selecting a driver from a scheduled queue comprises: selecting the driver from the scheduled queue and storing the driver in a cache of the processing unit when the cache of the processing unit has been initialized but a volatile memory has not been initialized; and selecting the driver from the scheduled queue and storing the driver in the volatile memory when the volatile memory has been initialized.