A multi-mode power supply system for a portable infusion device is provided, comprising a Battery I and an Battery II, the Battery I constantly charges the Battery II constituting a charging circuit, which adopts one of multiple charging modes including a basal-rate slow charging mode, a bolus-dose fast charging mode and a background charging mode depending on different drug infusion conditions； the Battery I powers the control unit independently, and the Battery II powers the driving unit independently； a unidirectional conduction circuit, a monitoring circuit and a detecting circuit are further comprised to ensure the normal operation of the power supply system under various circumstances. Any two of the Battery I, the Battery II, the driving unit and the control unit can be located in one housing, and the other two in the other housing； regardless of any particular combination, the coupling of the Battery I with the control unit and the Battery II with the driving unit are both implemented directly by a connecting element or connecting elements. This implementation of power supply meets both needs of basic functions and high power functions of the system with stability and efficiency.
