The main element of electron microwave devices with the electrostatic control and emission modulation (lasertron, femitron et cetera) is a strong-current electron cathode emitting the electron bunches. Usually the field effect electron cathodes (FEEC) are used as electron emitters. The increase of the full FEEC current value can be realized in using the high-efficient systems with a developed working surface-multi-tip emission systems (MTES). A technique is suggested for calculation of the electric field strength at the tip tops of a multi-tip field effect cathode consisting of the thin axially symmetric tips. The optimal distance between system tips is determined for given tips parameters such as the height, curvature radius et cetera. The optimal distance is shown to depend on the working point of a field effect cathode.