Objective To improve the key steps of direct volume rendering(DVR) method to obtain ideal semitransparent 3D visualization of medical images from 2D slices.Method An arbitrary data set was classified into a simple one and a complex one according to the boundaries existing within the data set,thereby a piecewise linear function was used to construct the transfer function(TF).Low-grayed voxels were regarded as a kind of material which did not radiate but do induce attenuation of sampling lights.The TF was adjusted according to the opacity distribution when one resampling process ends,and the rendering procedure was completed.Result Interior structures of tissues in different levels were rendered.Conclusion Multi-level visualization of 3D medical images for the semitransparent effect can be obtained by considering all the tissues in the data set as semitransparent materials.