A distance measuring device having a measuring range and configured for measuring a distance of at least an object located in the measuring range is provided. The distance measuring device includes a light emitting component, a diffusing component, an adjusting component and an image sensing component. The light emitting component is configured for emitting a light beam. The diffusing component is disposed on a transmission path of the light beam and is configured for transforming the light beam into a measuring light beam with a specific pattern to irradiate the object. The adjusting component is configured for adjusting an incidence angle and an incidence location of the light beam striking at the diffusing component. The image sensing component has a field of view covering the measuring range. The distance measuring device has a far measurable distance. A method for measuring distance and another distance measuring device are also provided.