Hi
I load several Dicom and use volume rendering to create 3D model.how can I save 3D model as a dicom file or mhd and raw?
Volume rendering is just a visualization mode, it does not create any model, segmentation, or labelmap. This has been discussed before on the forum, see for example: Save volume rendering as STL file.
You can save the loaded DICOM volumes as mhd/raw file by using menu: File / Save.
To save as STL, you need to first segment the volume using Segment Editor module. See tutorials here.