As a physician in a hospital affiliated with a medical university, I have been practicing medicine for twenty years and also teaching medical clinical internship for twenty years. Looking back on the experience and lessons learned from teaching medical clinical internship for twenty years, I deeply appreciate and realize that the fundamental of medical clinical internship is from theory to practice. Here I will talk about this issue from two aspects. A. The importance of theory to practice After a medical student enters a medical university, the first thing to do is to learn medical knowledge and theory, that is, the school classroom learning. Medical students have to learn normal anatomy, tissue embryology, physiology, biochemistry,, learn pathological anatomy, pathophysiology, diagnostics, and then clinical disciplines such as internal and external gynecology and pediatrics, and have learned other basic and instrumental disciplines such as English, computer, statistics, etc.. Having and mastering this medical knowledge and theory is only a paper exercise and does not allow for the diagnosis and treatment of real, concrete patients. To reach and treat specific patients, one must have a clinical internship under the leadership and guidance of a clinical instructor. Obviously, internship is the process of combining and applying one’s theoretical knowledge to clinical practice. Therefore, from theory to practice is the purpose of internship and the guiding principle of internship, which is the fundamental of internship. Clinical internship is a qualitative leap for medical students, as they are no longer facing books or inanimate experiments, but living patients. Whether medical students can apply their theoretical knowledge to specific patients through internship is the key to whether they can become qualified doctors. How to guide interns from theory to practice As a clinical medicine instructor, how to guide and help interns to turn their theoretical knowledge into practical ability? First of all, we should teach them how to contact and communicate with patients, and teach them to set up a good image of doctors for interns by their own words and example, focusing on everything for the sake of patients, starting from the condition, we have only one purpose, that is, to cure the disease and save lives! Only in this way will we get the patient’s understanding and active cooperation. Then, the supervising teachers lead the interns to jointly ask questions, conduct physical examinations, analyze various auxiliary examination results, make diagnoses and differential diagnoses, formulate treatment plans, perform treatment operations, observe treatment effects, and summarize experiences and lessons learned. In this way, through the step-by-step teaching of the supervising teacher, interns combine their medical theoretical knowledge into the diagnosis and treatment process of each specific patient step by step, so that their medical theoretical knowledge can move from abstract to concrete, from theory to practice, and truly participate in the diagnosis and treatment of actual patients. The supervising teacher should emphasize the importance of theoretical knowledge and guide the interns to contact each specific patient on the basis of their theoretical knowledge, analyze and think according to the correct diagnostic ideas, and gain clinical experience by treating one patient. As the interns’ clinical practice becomes more and more extensive and in-depth, their medical theoretical knowledge becomes alive, and when they go back to review those theoretical knowledge, their understanding and awareness will be on a new level. Therefore, teaching clinical practice is a very important and arduous work, which has an irreplaceable and important role in the growth of every medical student and is the necessary way to train qualified doctors. In the clinical teaching, from theory to practice is fundamental, and every teaching teacher should be engaged in teaching work with this principle, only in this way, our clinical practice will not deviate from the direction. Of course, there are many good ideas and methods for teaching clinical practice, which need to be constantly summarized and learned by our teaching teachers.