As an elastic control approach

switch migration plays an important role in multi-controller load balancing in software defined networking (SDN). In order to solve the problems of low migration efficiency and high migration cost in the existing schemes

this paper proposes Switch Dynamic Migration (SDM) Strategy based on efficiency optimization. We firstly analyze the composition of controller loads in detail

set up the load difference matrix to know the distribution of loads

and introduce a trigger factor

which is used to judge load balancing on controllers through comparing the overload threshold. Then

we formulate the migration objects

and introduce the migration efficiency model

which considers load balance rate and migration cost simultaneously to select the migrating switches and immigrating controllers. Finally

we set migration triplet to complete the migration mapping and achieve the efficient switch migration. Simulation results show this mechanism could lower controller response time effectively

reduce migration cost and improve controller throughputs.Besides

it keeps high load balancing rate and has good topology adaptability.