A convenient method,low-angle X-ray reflectivity measurement method,is presented to characterize the parameters of low-Z material layers in bilayer structures using X-ray diffractometer (XRD).Because the low-Z material optical constant is similar to the silicon(Si)substrate,the change of the low-Z material layer profiles is difficult to determine.Therefore,an ultra-thin metal layer is deposited as the Base Layer(BL)onto the substrate prior to the low-Z material layer.By choosing chromium(Cr)as the BL material,three Cr/C bilayer films with different C deposition times are fabricated and measured.After the simulation of the reflectivity curves,the density of C is approximately 2.25 g/cm3,while the deposition rate of C layer is 0.058 nm/s under our laboratory conditions.