Rehmanniae was chosen as the experimental material. The extraction method of catalpol in Rehmanniae was achieved via supersonic treatment followed by methanol extraction, and extraction time was decided thereafter. The results showed that degradation kinetics of catalpol in Rehmanniae during vacuum infrared radiation drying did not follow zero order or first order kinetics regulations. The degradation kinetics model of catalpol in Rehmanniae was established through introducing a parameter gT related to the radiation heater’s temperature, assuming that the parameters of degradation rate k agreed with Arrhenius equation. The test result showed that the model was a good fit for the experimental data.