A power optimization system including an optimization processing unit and a plurality of air conditioning's air-side apparatuses is disclosed. The system obtains a target comfort value when people enter a zone, and calculates an improving demand for the zone's indoor environment to approach the target comfort value. The system then collects an improving capacity of each air-side apparatus by operating in different working modes in the current indoor environment. After that, the optimization processing unit calculates multiple working combinations according to the improving demand and the improving capacities of the air-side apparatuses for the indoor environment to approach the target comfort value, and chooses a most power-saving working combination according to the basic power consumption of the air-side apparatuses.