Partial discharges in air in non-uniform electric field occur in surroundings made of high curvature elements. The equivalent electrode system, needle-plane refers both to external components of high voltage insulating systems and to micro sharpness in the internal structure of those systems. The ionization zone, accumulation of space charge and formation of corresponding current pulses depend on electrode configuration, voltage level, pressure, temperature and humidity of air. The assessment of pressure influence on discharge mechanism in non-homogenous electric field has been performed on the basis of empirical density distributions of discharge charges at different voltage levels, electrode distance, curvature of high voltage electrode and taking into account solid dielectric barrier in serial configuration. The measurement results obtained at variable voltage level yield the influence of electric field strength in the needle electrode zone. While increasing voltage, a deviation from normal distribution may be observed that reveals other forms of discharge.