The present invention relates to a polylactic acid 3D printing material and a preparation method thereof, which belong to the technical field of polymer materials. The polylactic acid 3D printing material of the present invention comprises the following preparation raw materials in parts by weight: (a) 40-95 parts of crystalline or semi-crystalline polylactic acid, (b) 5-60 parts of noncrystalline polylactic acid, and (c) 0-1.0 parts of a processing aid. In the polylactic acid 3D printing material, a weight of dextral polylactic acid represents 0.5%-8% of a total weight of the polylactic acid. According to the present invention, a polylactic acid 3D printing material with a good aging resistance property can be obtained, by selecting and using two kinds of polylactic acids with different optical purities as raw materials, rationally distributing the proportional relationship between the two, and defining the content of dextral polylactic acid. Studies show that the viscosity retention rate of the polylactic acid 3D printing material of the present invention reaches 70% or more after storage in a constant-temperature and -humidity chamber (at a temperature at 60°C and a humidity of 60%) for 12 days.