In the process of SDN multi-controller load balancing

controller selecting is rigid and switch migration is conflicting. This paper proposes a controller load balancing mechanism based on distributed policy

which is divided into three phases. Firstly

through collecting network information periodically

distributed migration decision domains are structured according to controller load conditions. Then the switches are migrated according to selecting probability. By balancing three costs included data collection

switch migration and state synchronization

the target controllers are determined. Finally

this mechanism sets the migration countdown to complete the switch migration and controller role conversion. Results show that

compared with the existing load balancing mechanism

this method could reduce the total network communication overhead

flow establishment time is shortened 0.14s averagely

controller resource utilization has been increased by 21.7%.