In order to better understand the gas breakdown occurring in high-voltage circuit breakers (HVCBs), it is necessary to know the dielectric breakdown properties of hot SF6 gas during the dielectric recovery phase. In this paper, the dielectric breakdown properties of hot SF6 gas contaminated by copper vapor are calculated based on the Boltzmann equation analysis, and the influence of copper contamination on such properties is studied in the temperature range of 300-3500 K at 0.6 MPa. The result shows that the existence of copper compounds increases the concentration of high-energy electrons significantly even for very low percentage (e.g. 1% Cu). The copper and its compounds also lead to the considerable rise in ionization coefficient and the decline in electron attachment coefficient of SF6-Cu mixtures. The critical electric field strength is reduced significantly at temperatures below 3000 K whereas enhanced marginally above 3000 K.