The invention discloses a preparation method of a collagen and polylactic acid composite hardening material. The preparation method comprises the following steps: firstly, selecting self-made or commercially-available polylactic acid with different molecular weights of 200 to 1000,000 and an alkali solution with the concentration of 0.01 to 2.0 mol/L according to the ratio of (1 to 100) to (100 to 1) (W/V), then soaking and washing for times under the environment of 25 to 45 DEG C, then filtering out solid and carrying out vacuum drying, wherein the pH value of the final washing liquid of the alkali solution is 5 to 9; secondly, heating the dried polylactic acid until the temperature reaches 40 to 150 DEG C and then softening to a flow state or dissolving an organic solvent into a liquid form; thirdly, uniformly mixing a collagen solution with a pH value of 4 to 8 or gel collagen with the polylactic acid according to the ratio of (1 to 100) to (100 to 1) (W/V), wherein the collagen concentration of the collagen solution or the gel collagen is 0.1 to 15 percent (W/V); finally, drying and forming a compound. The material prepared by the preparation method disclosed by the invention has the advantages that the material can be degraded and the degradation speed can be regulated; in addition, the material has certain toughness and is suitable for clinical restorative treatment of a plurality of tissue injuries.