The invention relates to a magnesian plastic material and a preparing method thereof. According to the technical scheme, materials are prepared according to a mass ratio of tetrabutyl titanate to tartaric acid to acetylacetone to polyethylene glycol 200 of 100: (5-8) : (0.5-1) : (1-2), and the materials are stirred to prepare a bonding agent. Materials are prepared according to a mass ratio of high purity magnesia-zirconia powder to gamma-aluminum oxide to cobalt oxide of 100: (5-10) : (1-4), the materials are subjected to ball grinding till the particle size is smaller than or equal to 80 micrometers, forming is conducted, and heat treatment is conducted under nitrogen atmosphere and at 1,500-1,550 DEG C for 1-2 hours; the materials subjected to heat treatment are smashed, grinded and sieved to obtain a material A with the particle size being 2-3 millimeters, a material B with the particle size being 0.088-1 millimeters and a material C with the particle size being smaller than or equal to 80 micrometers separately, the material A, the material B, the material C and silica power are added into a stirring machine, and the material are mixed to prepare a mixed material. Materials are prepared according to the mass ratio of the mixed material to the bonding agent of 1: (0.07-0.10), and the material are evenly mixed and aged to prepare the magnesian plastic material. The preparing method of the preparing method is low in cost and simple in technology, and the prepared product is long in retention cycle, big in volume density and high in compressive strength.