Using Masson pine as specimens, when drying mediums are overheated steam and hot-air respectively, preheating characteristics of wood under vacuum-floating pressure drying are discussed by measurement of internal temperature field and variation of moisture content during period of preheating. The relationship between drying medium conditions and drying rate of wood reveals that, firstly, compared with process of air-drying, time needed to be preheated under vacuum-floating decreased dramatically, meanwhile, the magnitude of condensation on the surface is relatively larger. Secondly, drying rate of wood under vacuum-floating pressure increases coupled with temperature of medium, reduction of absolute pressure, and raise of fluctuation rate of pressure. The sequence of factors contribution to drying rate is listed as following: temperature of medium (t) > fluctuation rate of pressure (f)> absolute pressure (p). Using Masson pine as specimens, when drying mediums are overheated steam and hot-air respectively, preheating characteristics of wood under vacuum-floating pressure drying are discussed by measurement of internal temperature field and variation of moisture content during period of preheating. The relationship between drying medium conditions and drying rate of wood reveals that, firstly, compared with process of air-drying, time needed to be preheated under vacuum-floating decreased dramatically, meanwhile, the magnitude of condensation on the surface is relatively wood under vacuum-floating pressure increases coupled with temperature of medium, reduction of absolute pressure, and raise of fluctuation rate of pressure. The sequence of factors contribution to drying rate is listed as following: temperature of medium (t)> fluctuation rate of pressure (f)> absolute pressure (p).