For a multi-fingered robot hand, the individual control over single joints cannot guarantee their fine collaboration. For achieving a high-precision synchronization, a theory of synchronous control is introduced to multi-fingered robot hands. This paper introduced a new model-free and cross-coupling control strategy. It had been tested on the humanoid robot fingers and showed high positioning performance. For realizing the mutual influence between the control of all joints, we establish the synchronization error by the differential disposal of adjacent actuator errors, then position errors and synchronization errors are incorporated into a unified control frame. Meanwhile, considering the complex dynamic formulations of the dexterous hand and the characteristics of the control system, a model-free, cross-coupled trajectory tracking method is introduced and the explicit dynamic modeling parameters is not necessary. Finally, we tested our method on a multi-fingered hand platform HIT/DLR-II. The results prove that the new method has superior performance over traditional non-synchronous approaches.