The invention relates to a method for preparing 75 mass percent solvent based cumyl peroxyneodecanoate and belongs to the field of preparation methods for initiators for synthesizing high polymers. The method is characterized by comprising the following steps of: adding cumene hydroperoxide into an alkaline solution; dripping neodecanoyl chloride into the obtained solution; after reaction, stopping stirring, and standing for 20 to 40 minutes, separating a mother solution, and washing a reaction product until pH value is 5 to 7; and adding an alkane solvent into the obtained reaction product, and stirring at the temperature of 0 DEG C for 1 hour; and thus obtaining the solvent based cumyl peroxyneodecanoate. According to the preparation method, a process is simplified, the complex requirements on reaction equipment are overcome, reaction is performed in a mild and safe environment, the quality and yield of the product are greatly improved, and the yield can reach over 95 percent. The quality level of the product is the same as that of products of the same kind in foreign countries.