The present invention provides a composite film containing polyethylene terephthalate, which comprises inorganic mineral powder, polyethylene terephthalate, an auxiliary plastic, and an auxiliary agent. The present invention also provides a method of preparing the composite film, which comprises internally mixing inorganic mineral powder, polyethylene terephthalate, an auxiliary plastic, and an auxiliary agent to form a composite soft material; configuring the composite soft material to be in a sheet shape; and stretching the composite soft material to form a composite film.