A method of manufacturing a thin film transistor, comprising: forming a pattern of an active layer and a gate electrode insulated from each other on a substrate, and forming a pattern of a source electrode and a drain electrode electrically connected with the active layer, respectively; wherein the active layer is a low temperature polycrystalline silicon thin film, and the low temperature polycrystalline silicon thin film is prepared by following steps comprising: forming an amorphous silicon thin film on the substrate; forming a pattern of a silicon oxide thin film covering the amorphous silicon thin film to be a thermal insulating layer, wherein a thickness of the silicon oxide thin film located at a preset region is larger than that of the silicon oxide thin film located at other regions other than the preset region to maintain the temperature of the amorphous silicon thin film located at the preset region during the crystallization so that the polycrystalline silicon formed at the preset region has a large crystal size; and the silicon oxide thin film located at other regions other than the preset region has a smaller thickness to avoid the temperature of the amorphous silicon thin film located at other regions being decreased sharply; irradiating the silicon oxide thin film by using excimer laser to allow the amorphous silicon thin film to form an initial polycrystalline silicon thin film, removing the silicon oxide thin film on the initial polycrystalline silicon thin film; hydrotreating the initial polycrystalline silicon thin film; and patterning the hydrotreated initial polycrystalline silicon thin film to remain the initial polycrystalline silicon thin film located at the preset region and remove the initial polycrystalline silicon thin film located at other regions other than the preset region so as to obtain a target low temperature polycrystalline silicon thin film, so that the thin film transistor is formed on the preset region. forming an amorphous silicon thin film on the substrate; forming a pattern of a silicon oxide thin film covering the amorphous silicon thin film to be a thermal insulating layer, wherein a thickness of the silicon oxide thin film located at a preset region is larger than that of the silicon oxide thin film located at other regions other than the preset region to maintain the temperature of the amorphous silicon thin film located at the preset region during the crystallization so that the polycrystalline silicon formed at the preset region has a large crystal size; and the silicon oxide thin film located at other regions other than the preset region has a smaller thickness to avoid the temperature of the amorphous silicon thin film located at other regions being decreased sharply; irradiating the silicon oxide thin film by using excimer laser to allow the amorphous silicon thin film to form an initial polycrystalline silicon thin film, removing the silicon oxide thin film on the initial polycrystalline silicon thin film; hydrotreating the initial polycrystalline silicon thin film; and patterning the hydrotreated initial polycrystalline silicon thin film to remain the initial polycrystalline silicon thin film located at the preset region and remove the initial polycrystalline silicon thin film located at other regions other than the preset region so as to obtain a target low temperature polycrystalline silicon thin film, so that the thin film transistor is formed on the preset region.