Digital image processing in medical applications is an important area. In this paper we present 3D reconstructions and 3D calculations for medical images. We have developed a medical image processing system (NAI200) to solve the problems of the need for 3D reconstruction or calculation images to be preprocessed. For example, zoom, negative, exponential, logarithm, histogram equalization, scale, filters, and other transfers are included. For the 3D reconstructions and 3D calculations the outlines of organs or focuses of disease are needed. In this paper we introduce some ways for autodrawing outlines. Different organs have different means. The entropy is an important method. But in the great majority manual operation may be most simple and precise. The stereo images of organs and focuses are reached, not only on the basis of slice images but also other ways. We describe these in this paper. About 3D calculation we first calculate the areas of slice images, then according to these areas to calculate volumes of organs or focuses. How to calculate a persons ventricular volumes, we also explain in this paper. All of these are reached by our NAI200 medical image processing system. Other functions of the NAI200 will be mentioned in this paper also.