Abstract: The combustion field is usually a complex system of gas-solid-liquid triphase coupling, and the results obtained from combustion diagnostic can support the researches to improve combustion efficiency and reduce pollutant emissions. In order to make the measurement results more accurate, it is urgent to develop advanced detection methods and detection systems. After several years of development, on-line mass spectrometry has the advantages of high sensitivity, fast analysis speed and wide detection range. It can be used for combustion flow field diagnostics under severe conditions such as high temperature and pressure, and can obtain more comprehensive and sensitive diagnostic information. Firstly, this paper summarized the development of key technologies, e.g., analyzer, ionization source, and sampling systems for on-line mass spectrometry in recent years. Secondly, the applications of on-line mass spectrometry on the measurement of flame component concentration and flame temperature in combustion field were enumerated. On this basis, the challenges and development prospects of the on-line mass spectrometry in complex combustion field diagnostics were summarized, which could provide reference for the relevant researchers.