A liquid crystal display device and a dimming controlling method thereof are disclosed. The liquid crystal display device includes a liquid crystal display panel, a drive circuit supplying a data pulse and a gate pulse to the liquid crystal display panel, a backlight unit divided into a plurality of block including light sources, and irradiating lights of which luminescence is controlled by the blocks, respectively, a controller analyzing an input video data by the block unit, generating a block dimming value based on a result of the analyzing, repeating a low pass filtering to the block dimming value to generate a local dimming value, applying a predeterminded global dimming value to an average of the local dimming value to generate a dimming signal, and a backlight driver generating a PWM signal for controlling a luminescence of the light sources by the blocks respectively according to the dimming signal to drive the light sources by the blocks respectively.