Mathematical model of mass and heat transfer about vacuum infrared radiation drying on Rehmanniae was built based on Fourier equation and Fick equation. The values or equation of model parameters were determined by theoretical analysis and experiments. By using finite difference method, mathematical simulations of sample temperature and moisture content under different drying conditions were carried out. The results showed that values of simulation and experiment fit well, the model could well simulate the changes of sample temperature and moisture content during drying and the influence of drying parameters on drying characteristics were illustrated by the model satisfactorily. 