A plasma enhanced atomic layer deposition (PEALD) system used to form thin films on substrates includes a plasma chamber, a processing chamber, two or more ring units and a control piece. The plasma chamber includes an outer and an inner quartz tubular units, whose central axes are aligned with each other. Therefore, plasma is held and concentrated in an annular space formed between the outer and outer quartz tubular units. Due to the first and second through holes, the plasma flow may be more evenly distributed on most of the surface of the substrate to form evenly distributed thin films and nano particles on the substrate. In addition, due to the alignment and misalignment between the first and second through holes, the plasma generated in the plasma chamber may be swiftly allowed or disallowed to enter to the processing chamber to prevent the precursor from forming a CVD.