The invention provides a manufacturing method for LTPS TFT substrate. After forming N+ areas on both sides of polysilicon layer, the first gate insulating layer, first gate, second gate insulating layer, and second gate are sequentially formed on polysilicon layer, and the second gate is wider than first gate to produce a low electric field region in the polysilicon layer to reduce leakage current; alternatively, forming first gate and first gate insulating layer, forming polysilicon layer and N+ areas on both sides of polysilicon layer, forming second gate insulating layer and second gate on polysilicon layer, the second gate insulating layer is thicker than first gate insulating layer and the second gate is wider than first gate, so that the second gate insulating layer sandwiched by the second gate beyond first gate and polysilicon layer is thicker and produces a smaller electric field, which simplifies process and reduce cost.