A night-vision optical device is provided, including a main body, a lens module, and a display module. The lens module includes an aperture element, a lens element, an electromagnetic driving assembly, an image sensor, and a digital signal processor. In response to an ambient light level around the night-vision optical device satisfying a predetermined condition, the digital signal processor (DSP) controls the night-vision optical device to enter a first mode, and controls the electromagnetic driving assembly to drive a first portion of a filter member to a first position to align an optical axis of the lens element. In response to the ambient light level not satisfying a predetermined condition, the DSP controls the night-vision optical device to enter a second mode, and controls the electromagnetic driving assembly to drive the second portion of the filter member to the first position.