The invention discloses a signal clamping device capable of clamping a signal with a clamp level that is set according to a frequency characteristic of the signal and a method thereof and a related optical storage system. The signal clamping device includes an equalizing unit, a determining unit, and a clamping unit. The equalizing unit is utilized for equalizing the signal and generating an equalized signal. The determining unit is utilized for generating an indication signal according to the equalized signal. The clamping unit is utilized for determining a clamp level according to the indication signal and clamping the signal with the clamp level.