The invention discloses a method for extracting a tannin extract by using a camellia oleifera shell, and application of the camellia oleifera shell to preparation of a composite material. The method comprises the following steps: crushing the camellia oleifera shell, adding water, an antioxidant and an ethanol exaction promoter, performing extraction and combining the extraction liquid; allowing standing still, settling and removing impurities, adding calcium and magnesium ions into supernatant liquid and performing complex-precipitation; taking complex precipitate, adding dilute sulfuric acid and performing replacement to obtain a tannin extract solution; concentrating and spray-drying the tannin extract solution to obtain the tannin extract with high tannin content; grinding the extracted camellia oleifera shell, and preparing a lightweight composite material by using the ground camellia oleifera shell, bisphenol A epoxy resin and a fatty amine curing agent. The method provided by the invention has the advantages of simple process, low cost, high tannin content of the extracted tannin extract, light color, safety, environmental friendliness and the like; the residual camellia oleifera shell after extraction of the tannin extract can be used for preparing the lightweight composite material. The camellia oleifera shell can be completely and comprehensively utilized, waste is changed into treasures, and good social, ecological and economic benefits are achieved.