Abstract: In-line flow meter is extensively applied in oil and gas fields in China, and it is faced with several problems.For example, its measurement results are of higher uncertainty, the phase holdup is greatly affected by gas content, and the measurement accuracy is restricted by the pipe diameter. In this paper, the current application situations of in-line flow meters in China were investigated and two factors leading to the increase of measurement uncertainty were determined.Then, the advantages and characteristics of domestic and foreign patents on in-line flow meters in recent 5 years were analyzed. The results show that the main factors leading to the higher measurement uncertainty of in-line flow meter are the frequent adoption of calculation model or empirical equation in the measurement principle and method, as well as the compositional change of multiphase flow. The research results provide the reference for improving the measurement accuracy of in-line multiphase flow meter in the future.