To fabricate X-ray absorption gratings, deep reactive ion etching and wet etching are used to fabricate grating structures on silicon wafers, and a liquid carrier, which is wet with the surface of grating structure, is used to bring the bismuth nanoparticles into grating structures in a dense arrangement. Then, a grating structure with the period of 42 μm and depth of 150 μm is filled. To show the performance of the fabricated absorption grating, a comparison with the bulk bismuth grating obtained by micro-casting method is provided. Moreover, the relationship between the grating period and the filling compactness through filling grating structures with periods of 24 μm and 6 μm is found. The scanning electron microscopy micrographs show the effectiveness of free settling method for the large-period grating structures. However, for the structures with 6 μm period, the filling compactness is not satisfied. The results illustrate that bismuth nanoparticles that their diameters are much less than the width of grating structures should be selected for the small-period absorption gratings. Furthermore, nanoparticles-based free settling method lowers grating cost and technique threshold, and allows the fabrication of large-area absorption gratings.