The present invention sets forth a power saving method and a power saving system applied in an optical disk drive. The power saving system comprises a central processing unit, a spindle motor, an optical pick-up unit, an analog portion of control circuits and a digital portion of control circuits. Each of the analog or digital portions of control circuits can be divided into several sets of circuits. Each set of circuits is coupled to an associated operation mode of the optical disk drive. The power saving system further comprises a power controlling unit for differentiating the specific sets of circuits not being used in the specific operation mode and powering them down. The sets of circuits not being used will be powered up while the associated operation mode in which they are required to operate is nearly started. The present invention also provides a power saving method of powering down the sets of circuits not being used relative to a specific operation mode of the optical disk drive.