A PVC rigid substrate, a preparation method therefor and a PVC rigid composite plate, wherein the PVC rigid substrate comprises the following raw materials in parts by weight: 40-50 parts of PVC, 75-150 parts of calcium carbonate, 0.6-1.0 parts of balance lubricant, 3.0-5.0 parts of stabilizer and 10-20 parts of CPVC. The PVC substrate has a high hardness, a very small heating size change rate which can be less than or equal to 0.05%. The impact resistance and toughness of a product may be greatly improved to facilitate the treatments that follow. Second, the PVC rigid composite plate has a high mechanical strength and a long service life; at the same time, the PVC rigid substrate can be prepared by using an extrusion method, which is very simple and easy to implement.
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