The heat transfer model between bolt and bolt hole of bolted flange sealing is established. Thermal radiation and thermal convection and thermal conduction are transformed into equivalent thermal conduction of air layer. Equivalent thermal conduction of different types of bolts under different temperature is computed. The result shows that thermal convection of air layer can be ignored completely of all types of bolts; equivalent thermal conduction change with temperature is linearity. Thermal conduction is the main way of heat transfer and the whole proportion of thermal radiation is less than 35%.