In order to develop a 3D visualization system for medical CT images which comply with DICOM standard, the authors study DICOM file format and methods of analyzing it, discuss the key technology of adjusting Windows Center/Windows Level of Medical CT images and 3D visualization methods, and describe the system's structure and approaches to implement every function module. Through developing 3D reconstruction software of medical CT images, surface rendering is compared with volume rendering.We succeed in implementing the visualization system for medical CT images which comply with DICOM standard. This system provides an intuitionistic way for diagnosing with medical images. The system is significant in clinical environment.