Abstract: On the basis of drying mechanism, this paper deals with the function of a heated-air hool used in the process of drying paper sheets. Guiding principles in designing the proess and the adventages and disadventages of this equipment are discussed. Variable; of air temperature and blast velocity to be chosen in a design are analysed and illustrated. Detailed description has been given to the process of the calculations in designing a heated-air hood. The limit moisture equivalent in the heated-air after recircu aion has also been evaluated. To reuse part of the outlet air in order to get the maximum benefit at the lowest cost is considered to be an effective measure in raising drying capacity in the production in China today.