The disclosure provides a polycrystalline silicon thin-film transistor and a method for manufacturing the same as well as a display device. The polycrystalline silicon thin-film transistor comprises: a substrate; an isolation layer formed on the substrate; and a polycrystalline silicon active layer formed on the substrate and the isolation layer, with two source-drain ion implantation regions being formed at both sides of the active layer, wherein the edges at both ends of the isolation layer are within the edges at both ends of the active layer. In the polycrystalline silicon thin-film transistor and the method for manufacturing the same provided by the disclosure, it is possible to increase the grain size of the active layer, improve the grain uniformity in a channel region thereof, effectively prevent deterioration of characteristics of the active layer caused by backlight irradiation, and improve the reliability of the device.