A DC-DC converting controller, coupled to an output stage including a phase node and an operation switch coupled between the phase node and a ground voltage, includes a pulse-width modulation (PWM) unit, a zero-level comparator and a threshold voltage generation unit. The PWM unit, coupled to the output stage, provides the PWM signal to the output stage for controlling the operation switch. The zero-level comparator has a first input terminal, a second input terminal and an output terminal. The first input terminal is coupled to the phase node. The output terminal, coupled to the PWM unit, provides a zero-current voltage to adjust the PWM signal. The threshold voltage generation unit, coupled to the phase node and zero-level comparator, provides the threshold voltage to the second input terminal. The threshold voltage generation unit dynamically adjusts threshold voltage according to a default voltage and the phase voltage on the phase node.