Rotor–fuselage coupling is a fundamental phenomenon that is essential for understanding helicopter dynamic behaviour, vibration characteristics, flight stability and integrity under various operating conditions through mathematical modelling. In this study, a coupled mechanical model is presented, combining the dynamics of rotor blade and rigid-body motion of the fuselage, via aerodynamic and inertial interaction forces. The beam theory is used to represent rotor deformation and the multi-degree-of-freedom equations are used to represent the dynamics of the fuselage. Modeling the interaction mechanism is done with a set of coupled differential equations that describe the exchange of forces and moments between subsystems. The numerical discretization and time integration algorithms are used to obtain stable and accurate transient solutions. The simulation results show that the proposed model can accurately predict the coupled vibration response, rotor-induced oscillation, and fuselage motion under some typical flight conditions. The framework developed is an efficient computation tool for helicopter dynamic analysis, vibration reduction strategies, flight control system design and structural optimization.