Abstract: The present disclosure provides a transistor and a manufacturing method thereof, a display substrate and a display device. The transistor includes: a base structure; an active layer on the base structure; and a gate electrode, a source electrode and a drain electrode that are all located on a side of the active layer distal to the base structure. The active layer includes a first region corresponding to an orthographic projection of the gate electrode on the base structure and a second region outside the orthographic projection. A surface of the base structure in contact with the active layer in the first region is not in the same plane as a surface of the base structure in contact with the active layer in the second region. The active layer in the first region has substantially the same thickness as a thickness of the active layer in the second region.