An automatic angle-adjustable display device and an angle-adjustable method are provided. The automatic angle-adjustable display device includes a screen, three wireless transmitting and receiving sensors, an angle adjustment mechanism and a control unit. The wireless transmitting and receiving sensors are respectively disposed at first, second and third positions of the screen. In response to a control signal issued from the control unit, the angle adjustment mechanism is driven to adjust the viewing angle of the screen with respect to the viewer. The angle-adjustable method includes steps of triggering the wireless transmitting and receiving sensors to emit these wireless signals, measuring first, second and third distances between the first, second and third positions of the screen and the viewer according to the reflected wireless signals, and adjusting the viewing angle of the screen with respect to the viewer according to these distance differences.