The blown film machine adopts A and B double main engines. After the machine head, the two materials of the two mainframes are formed into a three-layer film. The ABA structure has a strong blown film, hard hand feeling, good brightness, high output and strong puncture resistance. And the middle layer can be added with cheap materials to reduce costs.The three-layer co-extrusion blown film machine only needs two main machines, one squeezes the inner and outer layers (layer A), and one squeezes the middle sandwich layer (layer B) using recycled materials or other cheap materials, even adding 50% calcium carbonate. Its strength, weldability, and printability are unaffected, and the middle layer is cooled faster by the addition of calcium carbonate or low pressure polyethylene. Because the die of the three-layer co-extrusion blown film machine has three channels to reduce the pressure loss, the thickness of the film is more uniform, and the power consumption is more economical.