According to the research status of reliability evaluation of liquid engine, the reliability of flow measurement system is evaluated from two dimensions of performance reliability and structure reliability. The definition of performance reliability of measurement system is given. The measurement data are regarded as normal distribution, and the confidence limit of one-sided reliability is calculated by interval estimation. The definition of structural reliability of measurement system is given. According to the series reliability diagram of flow measurement system, the exponential life failure test information is transformed into binomial success or failure test information. The L-M (Lindstrom-Maddens) combined with look-up table and linear interpolation method is used to solve the lower confidence limit of structural reliability. The reliability evaluation method of measurement system has important reference significance for measurement technicians in the industry.