Abstract: Density resolution is an important parameter of CT system. Noise and density resolution were found to have a statistically significant positive correlation. To research the relationship between the scanning parameters(tube voltage, tube current, field of reconstruction and so on, which had significant influences on noise level) and density resolution, the disc phantom method was introduced and applied in the practical testing of an industrial X-ray CT under certain acquisition conditions. Then the results were demonstrated and discussed. At last, this paper discussed the parameters of the best density resolution under the same power.