The invention discloses a capacity optimization method for a power electronic multi-feed power system. The method comprises the steps: obtaining a rated capacity diagonal matrix of a power electronicdevice through the parameters of the power electronic device in the power electronic multi-feed power system, and calculating and obtaining a generalized short-circuit ratio of the power electronic multi-feed power system; calculating the sensitivity of the generalized short-circuit ratio relative to the rated capacity of each power electronic device; adjusting the rated capacity of the power electronic device according to the sensitivity, and recalculating the sensitivity of the generalized short-circuit ratio relative to the rated capacity of each power electronic device; continuously adjusting the rated capacity again according to the sensitivity until the sensitivity range meets a condition, thereby completing the capacity optimization of the power electronic multi-feed power system. The method provided by the invention is clear in physical mechanism, can remarkably improves the generalized short-circuit ratio of the power electronic multi-feed power system, improves the small interference stability of the system, and enables the power electronic multi-feed power system to operate stably.