The invention discloses a flame-retardant polypropylene material and a preparation method thereof. The flame-retardant polypropylene material comprises the following components in part by weight: 35 to 55 parts of polypropylene, 45 to 65 parts of modified basic magnesium carbonate, 0.2 to 0.5 part of antioxidant and 0.2 to 1 part of lubricating agent, wherein the preparation method of the modified basic magnesium carbonate comprises the following steps of: adding basic magnesium carbonate into a high-speed mixer; adding a coupling agent in an amount which is 1 to 4 percent based on the total mass of the basic magnesium carbonate to perform surface modification; and mixing at the temperature of between 60 and 130 DEG C for 20 to 40 minutes to prepare the modified basic magnesium carbonate. By performing the surface modification on the basic magnesium carbonate and through processing technology of the improved flame-retardant polypropylene material, the compatibility of the basic magnesium carbonate and polypropylene is improved, the raw materials are uniformly mixed, and the performance of the materials is improved; the basic magnesium carbonate has the advantages of wide resource and low cost; and the prepared flame-retardant polypropylene material has a good flame retarding effect.