The invention discloses a soft nanometer micro area flexibility-enhanced PET composite material and a preparation method thereof. The flexibility-enhanced PET composite material comprises the following components in mass percent: 80 to 93 percent of polyethylene terephthalate, 1 to 5 percent of a porous nanometer inorganic powder, 5 to 10 percent of liquid low polymers, 1 to 5 percent of polar grafted polymers, and a proper amount of an antioxidant. The method comprises the steps of grinding PET into a powder after the PET is cooled, soaking the nanometer inorganic powder through the liquid low polymer, so as to ensure that the nanometer inorganic powder is sufficiently soaked and absorbed by the liquid low polymer and to form a soft and elastic spherical nanometer structure, and improving the wetting property of the surface of the nanometer inorganic powder through the polar grafted polymer, so as to ensure that the nanometer inorganic powder can be uniformly dispersed in a PET matrix and a soft nanometer micro area can achieve the effect of flexibility enhancement in the PET. A PET sheet produced by adding the flexibility-enhanced composite material has excellent impact property, and maintains good optical property.