The invention relates to the field of power and electronic technologies, particularly to a power supply system with a stable loop comprising a PMOS transistor, a NMOS transistor, a first comparator and a voltage control circuit connected between a comparison terminal and the ground; wherein, a current-limiting acquisition port is configured to acquire on-state current of the PMOS transistor; and the current-limiting protection circuit outputs an voltage signal of the comparison result as the control signal of the pulse width modulation driver when the acquired on-current state of the PMOS transistor is less than a preset current value; and outputs a turn-off signal for turning off the pulse width modulation driver as the control signal when the acquired on-current state of the PMOS transistor is greater than a preset current value. The present invention has the advantages that relatively high loop stability can be ensured and high reliability is achieved.