The applied electric field (EF) has shown to have great influence on epileptiform firing. Epilepsy is a dynamical disease charactered by hypersynchronous firing. Taking the electrical characteristic of extracellular medium i.e. ephaptic transmission into consideration, we build a PR model in the presence of the applied electric field. V̄ DS out is the DC part of the voltage between soma and dendrite that electric field takes effect on PR neuron. In this paper we find V̄ DS out is the key parameter that affects the neuronal synchronization and use Unscented Kalman Filter (UKF) to estimate it, then based on key parameter we design a closed-loop control to desynchronize neuronal firing. It is found that the control can not only desynchronize neuronal network, but also can adjust the strength of applied electric field according to the degree of synchronization.