The system of coupled non-linear differential equations describing the transport phenomena inside dried kaolin and the boundary conditions for convective drying are proposed. The coupling between these two systems is introduced in the form of relationship between the moisture content and the relative humidity of drying medium near the surface. It gives a possibility of common modelling of the first and the second periods of drying. The Simulated results: drying curve, moisture content and temperature distributions are shown for kaolin cylinder. Simulations are carried out for constant drying conditions.