Dielectric properties of air plasma in a model circuit break were investigated. A chemically non-equilibrium (non-CE) model was used to simulate the arc dynamic behavior inside the nozzle during current zero period. Distribution of the critical breakdown electric field E-cr of hot air was derived from the electron energy distribution function by solving the Boltzmann transport equation, using calculated temperature, pressure and species composition. Then, the electric field at applied recovery voltage (E-a) was calculated. The probability of dielectric breakdown inside the nozzle can be predicted by comparing E-a and E-cr. The results show that neglect of departure from chemical equilibrium may lead to the overestimation of the dielectric recovery strength of circuit breaker arc during the first several hundred microseconds after current zero.