It is shown that, in HF and microwave power spectrum there’s a vague gap between theoretical, i.e. calculated with the help of convectional diffusion coefficient, and experimental rate of drying process, the latter being significantly lowed. The origin of the problem is due to vapour pressure gradient, its role, in mechanism of drying process up today investigated with white spaces and mistakes. Main characteristics of intensive drying process: the excessive vapour pressure, the vapour pressure time constant, the greatest possible value of evaporation rate are calculated. It is shown that the rate of drying process in wood under the internal heat generation may be significantly increased if its evaporation stage is preceded by the stage of heating in heat-insulating conditions.