A method, a system, and a terminal for adjusting screen brightness of the terminal includes the steps of obtaining a first screen display brightness value corresponding to ambient light brightness value, and obtaining illumination value of a camera and looking up a second screen display brightness value. When the second screen display brightness value is greater than the first screen display brightness value, the second screen display brightness value is set as the screen display brightness value. Namely, the display brightness is controlled by an Automatic Exposure Control (AEC) system, which increases displaying detail of image on the display.