Fiber Bragg Grating (FBG) thermal flow sensing technology has the advantages of low measurement threshold and high sensitivity, and has become a research hotspot in the field of flow measurement in recent years. In this paper, the principle of FBG thermal flow sensing is summarized, and the key and difficult problems in the current sensing technology are summarized (including sensor heating, structure design, temperature compensation and package sensitization), aiming at finding problems and looking into the future. Based on the typical research results in recent years, two kinds of heating methods and hot-wire sensing structure of electric heating and optical heating are analyzed. Temperature compensation and package sensitization are studied as special topics. Among them, temperature compensation aims to solve the cross- sensitivity problem of heat transfer and ambient temperature. Finally, the low sensitivity characteristics of the sensor technology under high flow are summarized and analyzed, and the possible research directions and related methods for improving the sensor sensitivity in the future are discussed.