Abstract: In order to analyze the influence of relative humidity, temperature and ambient absolute pressure on the wood EMC (equilibrium moisture content), the author chose small samples of Russian larch (Larix gmelinii Rupr.) as experimental material and measured their EMCs with the weigh method under the condition of relative humidity ranging from 40% to 90%, temperature ranging from 45℃ to 70℃ and ambient absolute pressure ranging from 30kPa to 70kPa in the vacuum tank. Then the influence of the relative humidity, temperature and absolute pressure on the equilibrium moisture content was investigated, respectively. Results indicated that: EMC of Russian larch increased from 6.13% to 13.18% as the relative humidity increased from 40% to 90% (70%, 50 kPa); EMC decreased from 16.60% to 8.40% as temperature increased from 45℃ to 70℃ (70%, 50 kPa); EMC decreased from 6.66% to 6.02% as ambient absolute pressure increased from 30 kPa to 70 kPa (50%, 70℃). Therefore, EMC of Russian larch under vacuum was affected as follows: it increased with the increasing relative humidity, decreased with the increasing temperature and ambient absolute pressure.