The invention provides a head-up display which includes an image source, a lens group with an adjustable focus, at least one mirror and a control unit. The image source is used for displaying an imagescreen and generating a corresponding image beam. The lens group with an adjustable focus is arranged on a moving path of the image beam. After the image beam is ejected from the lens group with an adjustable focus, the image beam is reflected by the mirror to a transparent screen, then the image beam is reflected by the transparent screen to enter a visual range of eyes of a user, so the user views a virtual image of the image screen, and an imaging position of the virtual image and the user are respectively located on different sides of the transparent screen. The control unit is used for controlling the imaging position of the virtual image and simultaneously adjusting the size of the image screen displayed by the image source with distances of the imaging position to the transparent screen, and the user's viewing angle of viewing the virtual image remains unchanged.