To some flexible spacecraft with a rigid center hub and two identical flexible plates,it can't be simulated accurately depending on the model in［2］because the plate's length causes big elastic displacement. So this paper presents a method with which the system simulating model is built by partitioning the flexible plate into several parts and introducing the floating coordinate respectively. The control rule is designed by taking the plate as a whole. And numerical simulation is done .The simulating results show that this method is very efficient for big displacement.