Abstract: Real-time fluid analysis has gradually developed and become the standard configuration used in many scientific drilling projects in China and abroad. Real-time fluid analysis is used mainly to determine on-line gas concentrations, monitor real-time drilling projects and their influence on fluid and to provide reliable geological parameters which are unattainable by other methods. Real-time fluid analysis can establish fluid geochemical profiles, determine isotopic composition, explore fluid change, identify gasses and any abnormality, and investigate the origin of fluid and its relation to geological activity. The applications and cases of real-time fluid analysis are introduced in this paper; this having become one of the required sub-projects of scientific drilling. The change of major composition determined by real-time fluid analysis system is summarized. The application of real-time fluid analysis would be incorporated into the research and development of scientific drilling which is usually requested by commercial projects. In addition, it is a fundamental necessity to constantly improve the long-term stability and reliability of analytical instruments and processes, particulary out in the field.