The present disclosure relates to a low temperature poly-silicon thin film transistor which possesses electrical characteristics and reliability, and a method of manufacturing the thin film transistor. The low temperature poly-silicon thin film transistor at least includes a gate insulating layer which is a composite insulating layer comprising at least three dielectric layers, wherein the compactness of each dielectric layer successively increases in order of the formation sequence thereof in the manufacturing process. Because the relation between the compactness of each layer of the composite insulating layer and that of the others thereof is taken into account according to the present disclosure, each layer in the composite insulating layer of the low temperature poly-silicon thin film transistor manufactured by the method according to the present disclosure can have enhanced surface contact characteristic and thin film continuity. The thickness of each layer in the composite insulating layer is further considered, so that the parasitic capacitance can be effectively reduced, and thus the response rate of the transistor can be improved. Namely, by improving the GI film forming quality, the electrical characteristic and reliability of the low temperature poly-silicon thin film transistor can be improved.