A method for reducing power consumption of a computer system in a working state is provided. The computer system comprises a processor, a memory and a chipset, and the processor is connected with the chipset through a processor bus. The method comprises classifying the power saving level of the computer system into a predetermined number of power saving modes, checking at least one power saving mode transition condition to determine whether to automatically raise the power saving mode of the computer system, and raising the power saving mode of the computer system by lowering a first voltage supply level of the chipset and a second voltage supply level of the memory and decreasing a first working frequency of the processor bus and a second working frequency of the memory. The power consumption of the computer system is further reduced in comparison with a normal working state when the power saving mode of the computer system is further raised.