The dynamic modeling and calculation of a large deployable space antenna truss are studied considering of gravity gradient. Based on the absolute nodal coordinate formulation method and the absolute nodal coordinate formulation reference node method, the rigid-flexible coupling dynamic model of the deployable structure is established. The energy-momentum conserving time integrator for calculating the dynamic equations is constructed by using discrete directional derivative. The orbital-attitude-deformation coupling dynamic response of the large deployable space antenna with multiple modules is obtained. The presented method is verified by comparing the results with those of the classic example and the commercial software ADAMS.