The present invention provides a flaky structure layered composite hydroxide and a preparation method thereof. According to the preparation method, a metal hydroxide, an oxide, a basic carbonate, a metal soluble salt and an alkali are adopted as raw materials, the addition speed of the alkali solution is controlled to prepare the flaky LDH, and the space confinement effect of the metal hydroxide, the oxide or the basic carbonate exists, such that the produced LDH flakes do not easily aggregate so as to finally obtain the LDH with a large specific surface, wherein the BET specific surface area is 130-200 m<2>/g and is much larger than the specific surface area of the ordinary LDH. According to the invention, the preparation method has characteristics of simpleness, no requirement of high temperature, high pressure and special equipment, rich raw material source and low cost; and the flaky structure layered composite hydroxide can be widely used in the fields of absorption separation, catalysis, polymer materials and the like.