The colors and the opacity of voxels in transfer function should be assigned in order to display hide interfaces (the interface of inner different mediums) in objects by direct volume rendering based on the general volume light model. Although the inner structure of objects is seen, it is not clear to see inner hide interfaces from the surface based on this model. One reason is that the general volume light model does not have the attribute of select transparency. The particles in 3D space are not penetrated by visible lights with one wavelength and absorb visible lights with another different wavlength.They can only absorb all kinds of visible lisible light in the same extent. Another reason is that it is short of surface information.A light model with the attribute of select transparency is used in the new algorithm,and the surface scatter which has nothing to do with the line of sight and the position of light source is put up into it.Meanwhile,the non-photorealistic rendering techniques are used to advance effects of inner hide interfaces.The hide interfaces and details are clearly displayed based on the new light model.