The paper introduces the concept of big data and its application in the medical field and makes SWOT analysis. The strengths include that the cloud computing can realize the storage of mass medical data, the data processing ability is powerful and the disease prediction based on data analysis is forward-looking and time-efficient. The weaknesses include the great difficulty in medical data collection, poor performance in data sharing, difficulty in integration, and lack of interdisciplinary talents. Regarding challenges and problems such as patients' privacy, data deficiency and false data, the opportunities include national policy support, development of information and sensor technology and huge demand in the medical field.