A transflective liquid crystal display device. A first substrate having viewing and peripheral areas is provided. The viewing area comprises transmissive and reflective regions. A backlight device is disposed under the first substrate, used to provide a backlight passing through the transmissive region. A power management controller connects the backlight device to control an intensity of the backlight. At least one photodetector is formed on the first substrate in the peripheral area, wherein the photodetector detects an intensity of ambient light above the first substrate, and then provides a corresponding signal to the power management controller to control the intensity of the backlight. According to the invention, the intensity of the backlight automatically becomes greater when the intensity of the ambient light becomes lower, and the intensity of the backlight automatically becomes lower when the intensity of the ambient light becomes greater.