The invention discloses a display device and a driving method thereof. The display device comprises a side-entry backlight, a liquid crystal display panel at the light outgoing side of the backlight, and a light control part positioned between the backlight and the liquid crystal display panel. The side-entry backlight comprises a light guide plate and multiple light emitting diodes arranged on a side edge of the light guide plate. The light guide plate is divided into multiple first areas, and the brightness of each area is controlled by at least one light emitting diode. The light control part is divided into multiple second areas, and at least one second area is covered by one first area. The brightness of each first area and the light transmittance of each second area are controlled by a display frame needed by a relative area of the liquid crystal display panel. Through adoption of the side-entry backlight, the display device becomes ultrathin. Moreover, the brightness of each first area and the light transmittance of each second area covered by one corresponding first area are controlled on the basis of the needed display frame, so a high dynamic contrast can be realized. Therefore, the display device that is ultrathin and exhibits a high dynamic contrast is obtained.