We investigate the effect of electric field on the properties of quasi-two-dimensional electron gas at the interface between ferroelectric oxide and insulating oxide in Ba0.8Sr0.2TiO3/LaMnO3 (BSTO/LMO) heterostructure. Interface conductivity measurements were performed by a four-point probe method before and after the effect of electric field on Ba0.8Sr0.2TiO3 ferroelectric film. We have shown that when a non-uniform electric field is applied to a ferroelectric film, we can turn off the state with high conductivity. Whereas under the influence of a uniform electric field on the ferroelectric film, we can turn on the interface state of high conductivity.