The present invention provides an open head mount display device and a display method thereof, relates to the field of head mount display technology, and can solve technical problems (such as a tedious operation, a poor display effect, an inaccurate position of the display image or the like) of the open head mount display device in the prior art. The open head mount display device of the present invention comprises: a display unit for providing a display image to user's eyes; an image acquisition unit for acquiring an image of an external object; an image analysis unit for analyzing and determining a position of the external object relative to the user's eyes in accordance with the image acquired by the image acquisition unit; and an image adjusting unit for adjusting the display image in accordance with an analysis result of the image analysis unit.