Disclosed is a low temperature polysilicon array substrate and its manufacturing method. The method includes: forming a light-shielding layer, a buffer layer and U-type polysilicon patterns successively on a glass substrate; doping channels of the U-type polysilicon patterns in the active area and then heavily N+ doping these U-type polysilicon patterns; forming a gate insulation layer and etching first via holes; forming a gate line, a source and lightly-doped regions of the N-type double-gate transistor; and heavily P+ doping U-type polysilicon patterns in the non-active area.