Considering the three-layer antireflection band being not wide enough, a new method to relize the design of broad band antirefleotive multilayer is proposed. Its total thickness is not changed. Using this method, equal-thickness four-layer antireflectivemultilayers have been designed successfully with the last reflectivity of less than 0.2%, antirefleotion band-width of 390nm. This paper represents design procedure, definite condition of antirefleotion and several examples of applied design. The result showed that this new method is much better than the classical antireflective mutilayers.