The invention provides a thin film transistor array substrate and a manufacturing method thereof. The thin film transistor array substrate comprises a substrate, an insulating layer, a power line, a data line, an initialized power line, a planarization layer and a pixel electrode, wherein the insulating layer is formed on the substrate; the power line, the data line and the initialized power line are all formed on the insulating layer; the planarization layer is covered on the power line, the data line and the initialized power line; and the pixel electrode is formed on the planarization layer. According to the invention, the initialized power line and the data line are on the same metal layer, while the initialized power line is not on the layer on which the pixel electrode is located, so that the initialized power line does not occupy the lining space of the pixel electrode, the pixel area can be maximized, thus the pixel aperture opening ratio can be improved greatly, the effective light-emitting area can be improved and the product performance can be improved.