Provided is a power saving control method and system for data storage devices or electrical equipment. Herein, data items are divided into groups according to required response times or access frequencies. The groups of data items are allocated to data storage devices or pieces of electrical equipment. A data storage device or electrical equipment to which data that may be accessed using a long response time at a low access frequency is set to a power-saving mode of a higher level. Consequently, the data storage devices or pieces of electrical equipment are provided with power-saving features of different levels. Eventually, energy saving can be achieved more efficiently.