The invention discloses a low addition type halogen-free and flame-retardant polylactic acid composite and a preparation method thereof. The composite is prepared from polylactic acid, a flame retardant, an optional flame retardant additive, an optional antioxidant and an optional lubricant, wherein the flame retardant is a phosphate, phosphamide, phosphoryl ester or phosphoramidate compound; the flame retardant additive is inorganic filler or organically modified inorganic filler. The preparation method of the polylactic acid composite comprises the following steps: polylactic acid is dried under vacuum and uniformly mixed with the flame retardant, the optional flame retardant additive, the optional antioxidant and the optional lubricant, and the mixture is placed in a twin-screw extruder for melt blending and extrusion pelletizing. The low addition type halogen-free and flame-retardant polylactic acid composite is low in adding quantity of the flame retardant, good in flame retardance and environment-friendly, and the mechanical properties are not reduced but are even increased; the preparation method is simple, convenient, fast, low in cost and suitable for industrial production.