The existence and overlapping phenomena of spatial expanding components have been discovered and investigated in designing diffractive optical elements.Based on the scalar diffraction theory,the forming mechanism of spatial expanding components was studied in detail from the angle of spatial frequency spectrum,and the corresponding conditions to eliminate their impacts were derived.Taking designing a 1-D beam shaping element with Gerchberg-Saxton(GS) algorithm as example,the relationship between the overlapping extent of spatial expanding components and the sampling period in the input plane was explored after the definitions of performance parameters to evaluate the qualities of beam shaping elements were given.These parameters include light efficiency and top non-uniformity.The simulated results validated the existence,overlapping and forming mechanism of spatial expanding components.