The fire hazard has frequently destroyed wooden cultural heritages. The discrete wood chips allow fire propagation quickly in practice. This study aims to clarify the effect of air-gap and thickness of wood chips in the fire propagation mechanism by experimental investigating the mass loss rate (MLR), flame spread rate (FSR), total burning duration (TBD) and the flame characteristic length (MFL). The 2 cm long and 10 cm wide wood chips were uniformly installed on a vertical sample holder. The air-gap distance and the thickness of wood chips changed from 1.0 cm to 3.0 cm and 1 mm to 4 mm, respectively. The flame spreads across with the wood grain orientation. The experimental result shows that FSR and MFL are sensitive to the air-gap distance. It is concluded that, TBD versus thickness of the sample is linear with an equation TBD (s) = 7.7 x thickness (mm) + 18.6. Concerning the fixed thickness of the sample, the TBD varies a little from the air-gap distance. The MFL increases to a peak then decreases to a low value as the thickness differing from 1 mm to 4 mm. It is observed that the air-gap makes little contribution to the TBD. The MLF history as the air-gap distance changing from 1.0 cm to 3.0 cm indicates that the distance of air-gap imposed little effect on the MFL. The a-MLR profiles mainly depend on the thickness of the sample.