An interactive model is developed to simulate dynamic behavior of pantograph-catenary systems. Vibrating responses of locomotive roof are directly inputted as excitations to the pantograph, which are obtained with the locomotive-track coupling dynamic model. Effect of locomotive vibrations on pantograph-catenary interactions is investigated for various cases. It is shown that the influence of locomotive vibrations upon the pantograph-catenary system dynamics is not negligible if the track geometric condition is not good, especially in high speed operation.