Concerning the flow rule tampering attacks and other single point vulnerability threats towards Software Defined Network (SDN) controller, traditional security solutions such as backup and fault-tolerant mechanisms which are based on passive defense defects, cannot fundamentally solve the control layer security issues. Combined with the current moving target defense and cyberspace mimic defense, a dynamic security scheduling mechanism based on heterogeneous redundant structure was proposed. A controller scheduling model was established in which the dynamic scheduling strategy was designed based on security principle combined with attack exception and heterogeneity. By considering the system load, the scheduling problem was transformed into a dynamic two-objective optimization problem by LA-SSA (Load-Aware Security Scheduling Algorithm) to achieve an optimal scheduling scheme. Simulation results show that compared with static structure, the dynamic scheduling mechanism has obvious advantages in cumulative number of exceptions and output safety rate, and the dynamic and diversity in the security scheduling mechanism can significantly improve the system's ability to resist attacks.The load variance of LA-SSA is more stable than that of safety priority scheduling, and the security imbalance is avoided, and the effectiveness of the security scheduling mechanism is verified.