A lithography system is provided and includes a light source device configured to emit a processing light beam onto the semiconductor wafer, to generate a penetrating light beam and a reflected light beam. The lithography system further includes a detecting module having a first detector and a second detector. The first detector is configured to receive the penetrating light beam to generate first power data, and the second detector is configured to receive the reflected light beam to generate second power data. The lithography system also includes a monitoring device configured to calculate absorbed power data of the semiconductor wafer according to the first power data, the second power data and reference power data of a reference light beam and configured to compensate for a pattern formed on the semiconductor wafer resulting from the processing light beam according to the absorbed power data and reference information.