Abstract: This paper designs a set of experiments to choose four different soil samples and studies the specific CT scanning parameters,which impact on the quality of rock and soil samples tomograms by use of direct method and indirect method and combining with the CT number changes.The parameters include the scanning voltage,the collimation mode,the filtering function,the samples size et al.The results showed that the scanning voltage and the filtering function have a great impact on rock and soil samples tomograms and CT numbers;the collimation mode and reconstruction matrix has little effect on the experiment results;The tomograms enhancement or inhibition depend on the chosen filter function properties,and have nothing to do with the soil.The following work provides the optimal principle of CT scanning parameters to improve the quality of rock and soil tomograms and obtain a relatively optimal CT numbers of rock and soil by means of the reasonable scanning parameters.