Abstract: With the further expansion of the scale of the user-side heterogeneous power Internet-of-Things device（UPID） in the distribution network integrating into the power system, it has brought a new cyber threat to the power system, namely the manipulation of demand（MAD） attack. In this context, it is necessary for the power system to manage and control the operation security of UPID in the distribution network. To this end, the software defined network（SDN） is integrated into the power cyberphysical system, and a dynamic routing strategy for the control instructions of UPID in the distribution network is proposed. First,the edge computing server is deployed in each substation for massive device data. Secondly, a three-stage dynamic routing strategy is constructed by considering the associated operating power and dynamic credit of control instructions, as well as the power system network structure. Finally, the SDN controller is used to realize the local control for control instructions. Simulation results show that the proposed SDN-based dynamic routing strategy can effectively avoid the malicious impact on the power system caused by large-scale abnormal actions of the UPID in the distribution network by refusing to forward low-credit control instructions, and provide a solution and implementation scheme for the power system to resist the MAD attacks.