The utility model relates to a disposable injection molding composite insulator, in particular to an insulator for a power transmission line. The disposable injection molding composite insulator comprises a core rod, a hardware tool with pipe-shaped connectors, a parachute-skirt-shaped insulator, and two sheaths arranged at two ends of the parachute-skirt-shaped insulator, wherein the sheaths are positioned on the surface of the core rod and firmly connected with the core rod, two ends of the core rod are respectively and firmly connected with a nozzle of the hardware tool with the pipe-shaped connectors at two ends thereof, a stepping circle is arranged at the nozzle of the hardware tool with the pipe-shaped connectors towards the parachute-shaped insulator, the sheaths at two ends of the parachute-skirt-shaped insulator at least covers the stepping circle at the nozzle of the hardware tool, and are firmly connected in a water-tight manner. By adopting the disposable injection molding composite insulator, not only the connection strength of the sheaths, the core rod and the hardware tool can be improved, but also the effect of water-tightness can be greatly enhanced becasue a plurality of combining surfaces are formed; and in order to further improve the effect of water-tightness, at least a circle of groove is formed on the outer rotating surface of the stepping circle. Thereofre, the combining surfaces are also added, thereby further improving the effect of water-tightness. In addition, the phenomenon of creepage can be effectively overcome through the parachute-shaped insulator according to the combination proposal for the parachute in size.