Two-parameter Townsend type current-voltage characteristic of corona discharge is substantiated by similarity theory methods I=A*U(U-Uc), (1) where parameters А and c U are found using statistical treatment of experimental data I(U) by the least squares method. As soon as these parameters depends on both the medium properties and the conditions of the corona discharge, particularly temperature T and pressure p in the interelectrode gap, there is a possibility to determine dependencies of corona discharge using the values of А и c U , which were found experimentally. In particular, the parameter of proportionality A, in its turn, is proportional to the dielectric permittivity ε of the gas and ion mobility k of the active electrode А= α∙ ε k, (2) where the constant α depends only on geometric parameters of the electrode system. (α- «installation constant»). Consequently, we can estimate the influence of dielectric permittivity and ion mobility on dependencies of corona discharge using the parameter A. The same is valid for the second parameter c U .  However, the main question is in what extent does the discharge is a corona-type discharge. The partial answer to this question gives the classical theory of the corona discharge: rectilinearity of reduced characteristics obtained from (1) by division by U is an indicator of the corona-type discharge. However, the answer is incomplete because though the reduced characteristics are rectilinear but the shift between them is non-informative. For this reason, at investigation of corona discharge instead of reduced characteristics, as indicator of the corona-type discharge (null hypothesis in terms of statistics), we introduce a more fundamental concept: a generalized characteristic. It is unique for all current-voltage characteristics and is obtained by transformation of the initial characteristic. It is represented by the angle bisector segment of the first quadrant: Y=X, 0<X<Xmax (3) here the non-dimensional quantities are denoted by subscripts (*) and dimensional, scalable quantities are denoted by subscripts (m). Thus, on the second phase of investigations of corona discharge we determine whether the discharge is a corona-type discharge with the help of equation (3). The equation (3) is a working equation for discharge process calculation as well as the equation of similarity which defines the conditions of similarity for corona discharge processes. Detailed investigations of corona discharge, conducted after verifying the null hypothesis, include various physical aspects of quantities А и c U in accordance with similarity equations (3) and (4). In particular, temperature dependencies, dependencies of discharge on pressure and mixture concentrations, and some other research questions are of special interest.