The present invention discloses a TFT array substrate and a manufacturing method thereof and a liquid crystal display device, which is aiming at lowering the resistance value of a common electrode and not diminishing the aperture ratio of pixels on the premise that the manufacturing cost is not additionally increased. The TFT array substrate includes: a substrate, a common electrode layer arranged on the substrate, a first insulating layer arranged on the common electrode layer and a plurality of pixel electrodes arranged in an array on the first insulating layer, wherein via holes penetrating through the first insulating layer are formed between adjacent pixels in some of a plurality of pixels, and common electrode lines are grown between rows and/or columns of pixels in some of the plurality of pixels, and in parallel with the common electrode layer below the first insulating layer through the via holes.