In architecture and urban design,solar energy plays an important role to save fossil energy and preserve environment.Passive or active use of this energy needs especial consideration in the preliminary stage of design to the probable shadows.This work will answer two questions:1)How is it possible to distinguish shadow need periods during a year in a specific climate? 2)How is it possible to produce shadow in hot periods without being deprived of pleasant sunshine in cold periods? In this regard,it will introduce the usage process and opportunities of“shading mask” of Olgyay as an easy and useful graphical method in six steps.At the end,different ways of using this method in design will be discussed.Several research projects that have been done in past 30 years will support the argument as examples of this method.