Explosive growth in medical information has exceeded human's cognitive skills and abilities. Traditional information management tools are challenged in satisfying people's needs of information service due to the diversity of clinical service environment and users. The existing medical service is difficult to meet the needs of the massive information processing and utilizing due to the development of intelligence and visualization of clinical service. This paper analyzes the collaborative cognitive feature between human and computer on the basis of scenarios of clinical process; presents an approach to information organization based on sematic; and proposes the technique of visual organization and interaction for large-scale medical data. Moreover, a user-centered visual analysis framework is proposed for clinical decision-making and reasoning. Finally an example of application is given to illustrate how to facilitate users to gain useful insights from the massive data by combining automated analysis techniques with interactive visualizations. Experiments show that visual analytics facilitate users to deal with information overloads and aid medical diagnosis decision.