Compared with conventional radiotherapy fields, small field has unique dosimetry characteristics such as high dose gradient, charged particle imbalance, and dose effect caused by source occlusion. These characteristics increase the difficulty of dose measurement and thus the uncertainty of clinical dose measurement, far exceeding the requirement of < 5% measurement error in ICRU 24 report. In recent years, with the development of new radiotherapy technologies, the minimum radiotherapy field can reach the millimeter level, and the single irradiation dose of hypofractionated radiotherapy can exceed 6 Gy. The larger dose gradient at the edge of radiotherapy field requires higher accuracy of dose measurement, and accurate small field dosimetry technologies have gradually become a research hotspot in the field of precision radiotherapy. In order to ensure the high accuracy of measurement, this paper reviews the research on small field dosimetry worldwide, and summarizes the key points of small field dosimetry. In this paper, the characteristics of small field dosimetry are introduced, and the current small field dosimetry technologies and optimization methods are summarized, including the optimization of detector selection and detector sensitive volume. The field output correction factor technologies are analyzed. In view of the difficulty in small field dosimetry, this paper provides suggestions on dosimetry based on clinical needs and the characteristics of medical linear accelerators. Our suggestions provide a scientific reference for small field dosimetry in clinical practice in radiotherapy institutions, and facilitate the development of radiotherapy dose verification.