A power saving method and system thereof is disclosed. When the central processing unit is under a non-snooping sleep state and a peripheral device sends a bus master request, a chip will drive the central processing unit waking from the non-snooping sleep state and entering a system management mode for executing an interrupt service routine that makes the central processing unit in halt status. The central processing unit is then driven to enter a snooping sleep state for snooping the bus master request. After the execution of the bus master request, the chip will drive the central processing unit to leave the snooping sleep state and return to the non-snooping sleep state for power consumption conservation.