The results of study of the defect structure variation process in the near-surface layers of lithium tetraborate (Li2B4O7) single crystals under the influence of an external electric field applied along the [001] polar direction are presented. Using the X-ray diffractometry with 2 ms time resolution the dynamics of the 004 and 008 diffraction peak parameters (angular position and integral intensity) variation was determined. Two types of processes caused by redistribution of the charge localized at the surface of the polar dielectric and the migration of lithium ions were revealed with different velocity and response time to the external field switching. The measurements were carried out at voltages providing a reversible character of induced effects. The use of two orders of diffraction with different X-ray extinction length made it possible to visualize space charge layers near the anode and cathode by the intensity variation of the diffraction peaks. Estimation of the effective thickness of the charged surface layer gives a value of 25 μm for lithium ions at the cathode and about 45 μm for lithium vacancies at the anode.