The preparation of pvc low-foaming dry blend is carried out on a standard heating and cooling mixing unit (this unit is a combination of a high-speed mixer and a cooling mixing unit). The mixing principle of the high-speed mixer is that the materials are rapidly scattered along the container wall under the impetus of the high-speed rotating stirring blade, and fall from the center of the container to form a vortex motion to achieve the effect of rapid mixing and uniformity. During high-speed stirring, when the materials are mixed, friction between the materials will be generated, that is, frictional heat will be generated at the same time. There will also be friction between the materials and the stirring blade and the container wall, and frictional heat will also be generated, as well as the heating source outside the container. Under the joint action, various additives can quickly infiltrate into the PVC resin and form a semi-gelled dry mixture. The principle of the cooling mixer is to pass cooling water through the outer jacket of the container, and under the low-speed stirring of the paddle, the dry mixture of about 110-120℃ is rapidly cooled to below 45℃ to prevent the hot material from agglomerating, decomposing and foaming. , The mixed dry blend discharged from the mixer should be sieved to remove agglomerates and molten particles for the next step of extruding and granulating, or directly extruding low-foaming products.