Abstract: Hard X-ray radiography is a technique widely used to diagnose inner information of matters. It is necessary to study the areal density(AD) resolution of hard X-ray imaging systems, because areal density is an important measurement of density, thickness and quality. In this paper, the model of AD resolution is derived and a new method of measurement for AD resolution is established. Using the self-made AD resolution plate, AD resolution limit of the hard X-ray imaging system, which is composed of scintillator, fiber bundle and CCD camera, is experimentally obtained under different exposures. Experimental data agree with the model curve in tendency, that is, the maximal AD resolution increases with the growth of the exposure, while the minimum AD resolution decreases.