Discloses is a brightness adjustment system and method, and a mobile terminal. The brightness adjustment system is used for a display device, and comprises: a distance measurement module configured to measure a perpendicular viewing distance from user's eyes to a display surface of the display device; and a brightness adjustment module configured to adjust the brightness of the display device to desired brightness based on the measured perpendicular viewing distance. The brightness adjustment system renders the display device, such as mobile terminal, etc., to automatically adjust the brightness based on the perpendicular viewing distance between the user's eyes and the display surface of the display device, satisfying requirements for display brightness.