A backlight unit, a control method thereof, and a liquid crystal display device are provided. The control method includes following steps: obtaining backlight data corresponding to each of the partitions, the backlight data including multiple bits of data; dividing a frame of a lighting process of each light-emitting unit of the partitions into a plurality of sub-fields having different durations, wherein each of the sub-fields corresponds to one of the bits of data; and outputting the sub-fields having different durations corresponding to each of the partitions in a preset order.