The authors observed temperature distribution in wood during pyrolysis in a sealed chamber while exposed to fire.They found that: 1) pyrogeneration and carbonization primarily occurred on the wood surface;2) the carbonized layer had asymmetrical thickness due to variations in the wood temperature;3) the carbonized layer shrank along the grain and along defects in the wood resulting in many gaps.This helped to increase and diffuse the temperature and gas pressure in the wood causing a significant influence on internal wood pyrolysis and temperature distribution.