Since big data become more and more common, and cross though our daily life. Big data got the advantage in the use in medical science, which is produce lots of medical data this days. Big data bring a new era in medical science. The application of big data in medical science has many aspects, such as preventive healthcare, diagnosis of disease, precision medicine, research development and public health etc. But there are still many challenges in the application now, such as the privacy and participation of the subjects, the accuracy of data, integration of relevant clinical guidelines and the training of big data user for medical applications. These issues should be discussed when applying big data in clinical medicine and health care.