Abstract: Based on the aerodynamic layout design method for the airframe/propulsion integration of airbreathing hypersonic vehicles, a coupling method of the internal and external flow fields was proposed in this paper. The flow field in combustor was solved by one-dimensional unsteady method considering finite-rate chemical reaction model, and the outer flow field of inlet and tail nozzle was calculated by two-dimensional CFD software. At the coupling interface between inlet and combustor, the parameters such as static temperature, static pressure and Mach number were transferred by one-dimensional average method. The hydrogen fuel combustor model developed by the National Aeronautics and Astronautics Laboratory (NAL) of Japan was used as an example to verify the internal flow field, and the integrated model of a typical hypersonic vehicle was used as an example to verify the coupling of the internal and external flow fields. The results show that the quasi-one-dimensional method based on finite-rate chemical reaction can simulate the combustion flow field more accurately. The coupling effect of internal and external flow fields can be calculated effectively by the proposed method, and the calculated pressure distribution of the rear body is close to the theoretical value. This method can provide an important reference for the performance analysis of the scramjet and the design of the airbreathing hypersonic vehicle with airframe/propulsion inttegration.