The present invention provides a TFT array substrate and a display device. In the TFT array substrate, a plurality of second fan-out lines, arranged in a fan-out region and respectively corresponding to a plurality of data lines, are arranged on a first metal layer; a plurality of first fan-out lines, arranged in the fan-out region and respectively corresponding to the plurality of data lines, are arranged on a second metal layer; the data lines and the second fan-out lines, as well as the second fan-out lines and the first fan-out lines, are connected via through holes; the surface resistivity of the first metal layer is greater than the surface resistivity of the second metal layer, thereby increasing the whole internal resistance of the fan-out line corresponding to each data line, and reducing the internal resistance difference between the fan-out lines corresponding to different data lines, so that no time sequence difference is generated when a data signal is provided for the plurality of data lines by the fan-out lines and the data signal is received by each data line, the product quality is effectively improved, the manufacturing process is further high in reliability, and the short-circuit risk of the fan-out lines is prevented.