The embodiments of the present disclosure provide a polysilicon thin film transistor and manufacturing method thereof, an array substrate, and a display panel. The method for manufacturing a polysilicon thin film transistor comprises: forming, on a substrate, a gate, a source and a drain, and an active layer. Forming the active layer comprises: forming a polysilicon layer on the substrate, which comprises a channel region and extension regions; performing ion injection process in the extension regions to form lightly-doped regions close to the channel region and a source region and a drain region; prior to or following the formation of the lightly-doped regions, employing halo ion injection process to form halo regions at the positions of the channel region which are close to the lightly-doped regions.