As a universal phenomenon in neural system, synchronization has attracted more attention in recent years. Moreover, synchronization control in neural system is considered as a method of curing mental diseases. However, the unknown factor in neural system may bring difficulties in the designation of controllers. In this paper, based on Lyapunov theory, we create a 'neuron observer' to control an abnormal neuron with unknown abnormal parameters, and transform the control signal to the external electric field to make the method available in clinical practice. According to the simulation result, this control strategy can accurately estimate the parameters in the reference neuron, and the character of the abnormal neuron can be accurately adjusted to normal condition. This method can be used as a potential therapy of mental diseases caused by abnormal changes of parameters in neural system.