The invention discloses a halogen-free phosphorus-containing flame retardant and a preparation method thereof. The halogen-free phosphorus-containing flame retardant has a structural general formula described in the specification, wherein -R1 to R12 are selected from one or more of alcoholic amino groups or phenolic amino groups, and the halogen-free phosphorus-containing flame retardant integrates a bio-based acid source and a carbon source, and is high in flame retardant efficiency, simple in synthesis process, pollution-free, green and environment-friendly in raw materials and low in cost.The invention also discloses a bio-based halogen-free flame-retardant polylactic acid material prepared from the flame retardant. The bio-based halogen-free flame-retardant polymerized emulsion with excellent flame-retardant property and better mechanical property is obtained by adding a small amount of the flame retardant and optionally adding a flame retardant aid and an antioxidant. When the addition amount of the flame retardant accounts for 0.5-8.9% of the mass fraction of polylactic acid, the limit oxygen index of the obtained bio-based halogen-free flame-retardant polylactic acid reaches 24-33%. The preparation method of the bio-based halogen-free flame-retardant polylactic acid material is simple, free of solvent influence, easily available in raw materials, easily controllable intechnological process and suitable for large-scale industrial production.