This paper compares non-chemical equilibrium effects in decaying arc in different gases and various conditions. The influences of the gas flow rate, the arc current, the pressure and the gas medium were investigated on the non-chemical equilibrium behavior. By increasing the arc current and the nozzle pressure, the non-chemical equilibrium effect will decrease. On the contrary, increasing gas flow rate enhances the non-chemical equilibrium effects. Additionally, the arc behaviors in different gas medium, which are air, N2 and O2 were investigated in this work. Since in different gas medium the reaction process will be quite different, even if the thermodynamic and transport properties of the gas medium are similar, the arc behaviors will be quite different. Therefore, here is a very important conclusion: in the previous works it was usually considered that the thermodynamic and transport properties will determine the arc behavior necessarily; the comparisons in this works clearly illustrate that the process and reaction path in the arc plasma will influence the arc behavior during the arc decaying phase dominantly.