The invention relates to preparation and application of a hydrotalcite-modified biomass material and a pyrolysis product thereof for removing tetracycline hydrochloride in a water body. Biomass is mainly prepared from agricultural waste, solid waste and the like and is wide in raw material source and low in cost. A preparation method comprises the specific steps that biomass suspension liquid containing bivalent metal salt and trivalent metal salt fully reacts with alkaline liquid, aging, filtering and cleaning with ultrapure water are conducted, and then drying is conducted to obtain the hydrotalcite-modified biomass material; lastly the hydrotalcite-modified biomass material is pyrolyzed through a tubular atmosphere furnace in a N2 atmosphere to obtain the pyrolysis product of the hydrotalcite-modified biomass material. The hydrotalcite-modified biomass material and the pyrolysis product thereof which are prepared through the method have the high removing capacity on tetracycline hydrochloride in the water body. The hydrotalcite-modified biomass material is easy to prepare and low in cost and is a cheap and efficient adsorbent. Through pyrolysis of the hydrotalcite-modified biomass material, the adsorption capacity of the hydrotalcite-modified biomass material is significantly improved, and the high application potential is achieved.