At present issue results of simultaneous study of Volt-Ampere characteristics (VACH) and energy spectra of ZrO 2/W heterostructure cathodes are discussed just under field emission terms. Firstly, needle shaped tungsten cathodes were coated by thin (~ 10 nm) film of ZrO 2 by means of thermo-field diffusion methods under ultra-high vacuum conditions. In this case the tungsten emitters were used as reference patterns and their characteristics were measured before the coating process. It is shown that VACH of coated emitters plotted in Fowler-Nordheim coordinates has non-linear character contrarily to “metallic” VACH. Such behavior of VACH may be attributed to complicated energy spectra obtained during VACH measurement and complex electronic structure of thin film. There are two peaks on the spectra plot with 3-5 eV distance between them depending on emission voltage. It is shown that energy spectra of coated cathodes have a regular fine structure, and all metamorphoses of the energy spectra are connected with variation of amplitudes of fine structure peaks while the positions of the peaks are constant during emission process for fixed thickness of zirconia layer. Considerable part of the work deals with ab. initio computer modeling of the field processes which can lead to rising of the fine structure and such a way attempts to explain behavior of energy spectra. It was shown that at least two-threshold potential barrier can lead to energy spectrum fine structure appearance. Model potential barrier of the eight atomic layers was considered in calculations relying on experimental pattern. Fine structure was recognized during computations.