To meet the need of precision for high power laser system, SHENGUANG Ⅱ, assembly of half-wave plate and polarizers is used to pre cisionly control the beam energy. The principles of attenuator assembly of half -wave plate and polarizers are discussed briefly. The characteristics of high p recision photoelectric detector and half-wave plate are measured by a special w ay. Then, automation technology is applied to intelligent adjustment. An energy precision of 2%(rms) is obtained in closed loop automation simulation experiment s.