Fingertip glucose testing is an important blood glucose measurement because it helps patients understand their blood glucose levels. However, more frequent fingertip measurements cannot provide you with 24-hour continuous blood glucose information. Fingertip blood glucose measurements are done at a single point in time, and they do not show trends in blood glucose levels. Therefore, even the most aggressive frequent glucose measurer cannot detect those occasional hyperglycemia or hypoglycemia, especially during the night time. The ambulatory glucose monitoring system (CGMS) is an innovative technological breakthrough in the field of blood glucose monitoring. It reflects the blood glucose level by continuously monitoring the glucose concentration in the subcutaneous intercellular fluid. It is known as the “Holter” of blood glucose monitoring. CGMS consists of a glucose recorder, information extractor, sensor, cable and glucose analysis software, etc. The glucose recorder is connected to the sensor through a cable, receives an electrical signal every 10 seconds, stores an average value every 5 minutes, and automatically records 288 glucose values every day. The CGMS can automatically record patients’ blood glucose values and related events (medication, insulin, diet and exercise and others), and download complete single-day blood glucose graphs, multi-day blood glucose graphs, blood glucose graphs before and after meals, blood glucose graphs of specific time periods and statistical data table reports through the computer, from which you can understand comprehensive blood glucose information, discover many high blood glucose, low blood glucose and the pattern of blood glucose fluctuations that are not easy to find normally, and understand the relationship between oral medication, insulin, diet and exercise and blood glucose. It also provides valuable clinical basis for the formulation and evaluation of rationalized and individualized glucose-lowering treatment plans, and effectively helps to educate diabetic patients and improve their understanding of and compliance with diabetes. Through the ambulatory glucose monitoring system (CGMS), physicians will learn information about patients’ blood glucose fluctuations, including intra-day blood glucose fluctuations, inter-day blood glucose fluctuations, meal-related blood glucose fluctuations and hypoglycemia. Thus, a reasonable and personalized blood glucose control plan can be evaluated and formulated. CGMS provides comprehensive blood glucose information, especially in monitoring blood glucose fluctuations, and is an indispensable tool for improving diabetes diagnosis and treatment.