The invention discloses a preparation method of a bamboo-pulp cellulose and poly(N-vinylformamide) composite flocculating and decolorizing material. Key points of the adopted method lie in that a bamboo-pulp pulp board is subjected to shearing off, water scrubbing, drying and pulverization treatments to pulverize cellulose; a refrigeration treatment is carried out by adopting sodium hydroxide and a urea solution to dissolve the cellulose; the graft copolymerization between the dissolved cellulose and poly(N-vinylformamide) is initiated through free radicals to prepare and obtain a composite flocculating and decolorizing material product. The preparation method of the bamboo-pulp cellulose and poly(N-vinylformamide) composite flocculating and decolorizing material uses the bamboo-pulp cellulose as a raw material while guaranteeing that the product has favorable flocculation and decolorization effects, expands the range of raw materials for preparing the flocculating and decolorizing material, not only can decrease production cost and improve economic benefit, but also can broaden an application field of a bamboo-pulp fiber, increases the added value of the product, and has obvious social benefit and economic benefit.