A manufacturing method for LTPS TFT substrate is disclosed. Through performing two etchings on the gate metal layer, ion heavy doping and ion light doping of the polysilicon active layer are performed in a self-aligned manner such that the LDD structure of the polysilicon active layer is symmetrically distributed on two sides of the gate electrode, which is beneficial to improve device characteristics, is more stable and reliable than the conventional technology, and can reduce the number of process masks, save mask cost, operation cost, material cost and the time cost. The thinning process of the gate insulation layer can reduce the thickness of the gate insulation layer corresponding to the heavily doped region of the polysilicon active layer, so that the ion implantation efficiency can be effectively improved.