Embodiments of the invention disclose a thin-film transistor having a channel structure that has an increased width-length ratio and a manufacturing method thereof, a display substrate and a display device. The thin-film transistor comprises a gate, a gate insulation layer and an active layer stacked on a substrate, the active layer is formed therein with a source region, a drain region and a channel region, a surface of the active layer facing the gate insulation layer is at least partially formed with a non-planar surface in the channel region, such that the non-planar surface of the active layer has a tortuous shape in a width direction of the channel region.