When synchronous belts are engaging with sprockets, they have complicated dynamic behaviors because of their complex composition. The inertial and damping forces of synchronous belt cannot be neglected when the belt is in a state of high acceleration or high-speed transmission, and these factors considerably influence the selection of belt type and the overall design of the system. The pretensioning force also significantly influences the stress state and fatigue life of synchronous belts, so a pretensioning analysis should be carried out before the elastic dynamic analysis. Our goal in this work is to study the precise influence of inertial and damping forces on the dynamic performance of synchronous belts under high acceleration or high speed. Toward this end, the pretensioning and elastic dynamic analysis of a synchronous belt drive system using two-dimensional beam elements without shear deformation based on the absolute nodal coordinate are studied in this paper. To verify the results of the elastic dynamic analysis, a rigid–flexible coupling dynamic simulation of synchronous belt drive system with the dynamic software RecurDyn is also carried out. The results are presented in the form of stress curves for the synchronous belt.