The disclosure discloses a backlight unit and a liquid crystal display comprising thereof. The backlight unit comprises a light guiding plate comprising a plurality of light guiding plate units, which are arranged as a matrix along longitudinal and traversal directions, with line-shaped gaps extending respectively along traversal or longitudinal direction existing between two adjacent light guiding plate units; a light source provided at a side of light guiding plate; and a diffusing sheet provided above the light guiding plate. At a position corresponding to the line-shaped gap between the two adjacent light guiding plate units, the diffusing sheet has a shape of line-shaped projection, and the line-shaped projection has a projected direction in a direction of the light emitted from the light guiding plate unit. According to the disclosure, the uniformity of the backlight may be improved.