The influence of different factors on Paschen-curve and appearance of their abnormality in a form of three-value dependence a discharge firing voltage versus pd is analyzed by numerical simulation. The abnormality is observed when the coefficients of cathode secondary emission and electron reflection from an anode are low and the discharge is firing at higher pd with frequent charge exchanges of ions. The important role of electrons reflected from an anode in range 1-100 kV and fast atoms reflected from a cathode at voltages above 10 kV is revealed.