A method for manufacturing a LTPS TFT substrate is provided. Buffer layers are respectively provided in a drive TFT area and a display TFT area and have different thicknesses, such that the thickness of the buffer layer in the drive TFT area is larger than the thickness of the buffer layer in the display TFT area so that different temperature grades are formed in a crystallization process of poly-silicon to achieve control of the grain diameters of crystals. A poly-silicon layer that is formed in the drive TFT area in the crystallization process has a large lattice dimension to increase electron mobility thereof. Fractured crystals can be formed in a poly-silicon layer of the display TFT area in the crystallization process for ensuring the uniformity of the grain boundary and increasing the uniformity of electrical current. Accordingly, the electrical property demands for different TFTs can be satisfied.