The invention belongs to the technical field of inflaming retarding modification of high polymer materials, and specifically relates to a method for preparing microcapsule red phosphorus inflaming retarding polylactic acid. The method comprises the following steps of: pre-treating red phosphorus, and preparing melamine formaldehyde resin prepolymer solution; adding the pretreated red phosphorus, distilled water which is 2 to 20 times of the quantity of the red phosphorus and a dispersing agent which is 0.5 to 2 percent of the quantity of the red phosphorus into a reaction vessel; stirring the mixture and heating the mixture to a temperature of between 60 and 90 DEG C to obtain a red phosphorus suspension; then adding metal salt solution into the suspension; adjusting the pH value of the system by using ammonia water; keeping the temperature and stirring the mixture; adding the mixture into the melamine formaldehyde resin prepolymer solution so that the resin content in the solution is 22 to 94 percent of quantity of the red phosphorus; adjusting the pH value of the system to between 4 and 5 by using glacial acetic acid, keeping the temperature and stirring the mixture; after the reaction is finished, cooling and filtering the suspension, washing the suspension to be neutral, and drying the suspension to obtain inorganic-organic double-layer coated microcapsule red phosphorus; grinding the obtained microcapsule red phosphorus, and drying polylactic acid to remove the moisture; and adding the obtained microcapsule red phosphorus and the polylactic acid into a drying container, mixing the obtained microcapsule red phosphorus and the polylactic acid evenly, and melting and blending the mixture to obtain the required product. In the product, the polylactic acid accounts for 65 to 75 percent and the microcapsule red phosphorus accounts for 25 to 35 percent. The method has a low cost and a simple and environment-friendly preparation process.