The invention discloses a method for preparing C11 perfluoroketone. The preparation method comprises the following specific steps: adding a hexafluoropropylene oxide trimer, a reaction solvent and basic salts into a reaction kettle, and carrying out stirring reaction at the temperature of 0DEG C for 1 to 2 hours; then introducing perfluorodipropionyl peroxides, raising the temperature to 75 to 155DEG C, and carrying out stirring reaction for 1 to 8 hours; cooling after reaction pressure has no change, opening the reaction kettle, separating out subnatant and distilling to obtain a product C11 perfluoroketone. According to the method disclosed by the invention, an environment-friendly treatment process is simplified, raw materials are easily obtained, the reaction yield is increased, simple operation and easiness in purification are realized, and enlarged production can be performed; the hexafluoropropylene oxide trimer, the perfluorodipropionyl peroxides and the basic salts are used as initial reactants; the initial reactants are subjected to one-step reaction to obtain a finished product; the reaction temperature is lower, the reaction speed is high, and the reaction yield is higher, so that the enlargement of the compound is easily realized.