An open-loop inductor current emulating circuit is provided. A current sensor circuit senses a current flowing through a first terminal of a low-side switch to output a current sensed signal. An emulation controller circuit outputs a plurality of charging current signals according to currents of a plurality of rising waveforms of the current sensed signal. The emulation controller circuit outputs a plurality of discharging current signals according to currents of a plurality of falling waveforms of the current sensed signal. A charging and discharging circuit generates a plurality of charging currents according to the charging current signals, and generates a plurality of discharging currents according to the discharging current signals. The charging and discharging circuit alternatively outputs the charging currents and the discharging currents to the capacitor to charge and discharge the capacitor multiple times, thereby achieving a purpose of emulating an inductor current.