Abstract: Ray tracing for volume rendering (RTVR) is one of the most efficient ways to visualize 3D scalar data,and has been widely used.The large amount of data needs an economical storage scheme.In this paper,we deduce the ray-tracing equation and chain-relations of non-isotropic resolution data field under Cartesiane-coordinate system.We also study its application in 3-dimensional ultrasonic imaging based on series CT slices data from NDT.Examples show that the method used by us can reflect the original data really and be used to classify different kinds of materials.The resulted image is quite good with BIG objects,though blur with SMALL ones due to the lower resolution of the original data.