The dynamic change of moisture ratio and sample temperature during desorption drying in freeze drying of cooked beef slice were simulated, and the optimal operation conditions were determined through the analysis of the drying rate and energy consumption. Mathematical models were established for desorption time, sample center temperature and sample surface temperature while the moisture of sample was dehydrated during the desorption drying. Moisture ratio was taken as independent variable. On the assumption that the moisture ratio descended from the terminal moisture ratio of sublimation drying (10.0%) to terminal moisture ratio of desorption drying (0), dynamic changes of the moisture ratio, surface and center temperatures of the samples with time during desorption drying in freeze drying experiments were simulated successfully. The experimental conditions were as follows: chamber pressure was 10 Pa, heating board temperature was 80℃, the sample thickness were 6, 8, 12 and 15 mm, respectively, Moreover, the moisture ratio, center and surface temperature changing and desorption periods of cooked beef slice in thickness of 7, 9, 10, 11, 12, 13, 14 mm during desorption drying were forecasted. The validation experiments were conducted and the results showed that the comparative errors between forecasted and measured moisture ratio were lower than 10%, and absolute errors between forecasted and measured centre temperature of drying sample were lower than 5℃. It can be concluded that the predictive model can be applied to simulate and forecast the changes of operational parameters during desorption drying of cooked beef slice in thickness of 6-15 mm in freeze drying. Compared comparative time-consuming and efficiency of desorption drying, the highest productivity and the lowest energy consumption to produce a certain quantity of products are obtained when sample thickness is 6 mm.