Aiming at the restriction of the number and the thickness of elements used in the inertial confinement fusion (ICF) system, especially in the final optics assembly, and utilizing the characteristic of easy integration of diffractive optical element(DOE), a new means to fabricate color separation grating (CSG) and beam sampling grating (BSG) on two surfaces of one fused-silica substrate with two-surface exposure method is presented. Thus the functions of harmonic wave separation and beam sampling are realized through one silica plate. The masks of CSG and BSG are fabricated by photolithograph and e-beam direct writing method, respectively, and the ion beam etching method is used in fabricating the combined CSG-BSG element. The experimental results show that the parameters such as energy utilization ratio, color separation ratio and sampling efficiency for 3ω harmonic wave are in accordance with those of separated CSG and BSG elements, which achieve the basic technical requirements of the final optics assembly of ICF driver.