The flue gas flow is an important parameter to determine the capacity of waste heat boiler in offshore oil production facilities. In this paper, the excess air coefficient α is calculated by measuring the combustion products (such as O2, RO2, etc.) of gas fuel by gas analyzer on the basis of given gas fuel composition and fuel characteristic coefficient, and then the flue gas flow of gas turbine is calculated . The results show that under different loads, the α value of gas turbine varies from 3 to 7, which is significantly greater than that of boiler. This measurement method has important reference value for engineering application of gas turbine flue gas waste heat recovery in offshore oil production facilities.