The radial solids fraction profiles in the inlet region of a high density circulating fluidized bed (HDCFB) are studied by a dual-beam optic density sensor. Three kinds of inlet structures are employed to examine the axial developing process of the profiles. The acceleration effect of solids is analyzed by comparing the cross-sectional average solids fraction obtained by the density sensor and differential pressure method. The results show that the radial, solids fraction profile is largely influenced by the inlet structure. The length for the inlet effect region is no more than 2.5 m above the air injection.