Most of the devices based on ferroelectric materials used z-geometry to switch the ferroelectric polarization. However, for a variety of optical and microwave devices, the principle of which is based on the interaction of electromagnetic waves with polarized dielectric is more preferably used a planar geometry of the application of an electric field. Polarization behavior in the application of an electric field is crucial. Fabrication of two-dimensional photonic crystals based on ferroelectric thin films is necessary for expansion of the practical application of nanoscale ferroelectrics. For electro-optic modulators and phase shifters ferroelectric films with high dielectric constant, low switching times and low losses are required, and it is necessary that the films were homogeneous with respect to these parameters. At the same time, investigating the distribution of polarization states on the surface of the sample is needed in the area of the electrodes, as well as the dependence of the polarization state on the applied external electric field. In this report, to clarify the limits of applicability of the developed models and provide the information necessary to predict the properties of photonic crystal structures, local experimental studies of the ferroelectric polarization switching are presented in the perforated ferroelectric films as well as mapping of the polarization state, depending on the parameters of the applied electric field and comparison of data switching characteristics with the non-perforated films. Epitaxial BST film with a thickness of 1 micron was deposited by RF sputtering on MgO (100) substrate. For applying a constant electric field the interdigital electrode system (IDT) was made on the surface of the sample with a gap of 2 μm, which allows to apply the field in the film plane. 2D photonic crystal structure (PhC) was formed in the gaps between the electrodes by focused ion beam etching (Quanta 3D, FEI Technology); the hole diameter was 880 nm, the depth of 1 μm. Investigation of polarization was performed using nonlinear optical microscopy based on the proportionality of optical second harmonic (SH) intensity to the square of the ferroelectric polarization, consisting of two parts: switchable and non-switchable [1]. The observed increase in polarization as compared with the non-perforated film may be associated with the formation of new local fields in the PhC under the influence of the ion beam. The resulting domains are pinned to the inner surface of the air channel, thus reducing switchability of polarization. Nevertheless, the relative change of polarization upon application of the field is higher than for the unperforated film. The data obtained should be taken into account when modeling the properties of photonic crystals based on ferroelectric thin films and in the development of electrooptic modulators and other switching devices based on them.