A new configuration of spacecraft was designed for deep space exploration. Due to difference of configuration and mass distribution， the traditional dynamic modeling method is no longer suitable for this configuration. In order to satisfy the requirement of overall design of dumbbell spacecraft， an efficient and accurate dynamic model must be established for this configuration. In this paper， based on a small deformation assumption， a rigid-flexible coupling dynamic model of dumbbell spacecraft was established using a forward recursive method in the floating frame of reference formulation. The orbit-attitude-deformation coupling effects were taken into account， and all the high-order coupling terms of deformation were kept. The numerical simulations of the "rigid body-truss-rigid body" model proposed in this paper and two existing models were carried out， indicating that the inertia moment of the end object cannot be ignored， but the proposed model can capture the rigid-flexible coupling dynamics characteristics of dumbbell spacecraft well. This paper will provide an important technical support for the overall design， especially for the controller design of dumbbell spacecraft.