The invention discloses a high-strength polylactic acid bone fixation material and a preparation method thereof. The high-strength polylactic acid bone fixation material is characterized in that a multifunctional long-chain flexible branching agent is prepared by virtue of reaction of polyether and aliphatic isocyanate and is combined with a multifunctional epoxy compound for use, and long-chain branched polylactic acid is prepared by virtue of a simple, convenient and feasible reactivity processing method, so that the entanglement degree of chains among polylactic acid molecules is increased,and the tensile property of polylactic acid is improved; and by introducing a polyether long chain, polylactic acid is endowed with relatively good impact toughness, and a high-power uniformly-orientated polylactic acid material is prepared on that bases by virtue of a double-shaft solid phase thermal stretching method, so that the mechanical strength of the polylactic acid material as the bone fixation material is substantially enhanced, and meanwhile, the biocompatibility of the polylactic acid material is improved.