Abstract: OBJECTIVE To compared the effect of different drying methods on drying characteristics, water effective diffusion coefficient and biased activation energy of Codonopsis Radix and to definite 3 different drying methods of varying temperature(45-55-60, 60-55-45, 60-45-60℃) and 3 constant temperature(45, 55, 60℃) on drying characteristic curves of different commercial grades of Codonopsis Radix. METHODS Used R², χ² and RMSE as evaluation indexes, 10 typical drying kinetic models were selected to fit the drying curve of Codonopsis Radix, and the effective moisture diffusion coefficient and biased activation energy under different drying method were calculated. RESULTS It was found that the Midilli model could well describe the drying process of different commercial grades of Codonopsis Radix, the water ratio of Codonopsis Radix showed an exponential downward trend. If the initial drying temperature was set above 55℃, the maximum drying rate could be reached within 2 h. And commercial grades temperature had certain influence on the effective water diffusion coefficient of Codonopsis Radix. Under the same temperature condition, the average speed of moisture migration during drying of Codonopsis Radix was:first-class> second-class>third-class, and the D_effwere 10.433 9×10^-8, 5.545 2×10^-8, 2.249 6×10^-8·m²·s, respectively. The calculated bias activation energy of Codonopsis Radix was 2.943×10⁴-4.378×10⁴ J·mol^-1, the order of bias activation energy of different drying methods was as follows:60-55-45℃ variable temperature<60-45-60℃ variable temperature<45-55-60℃ variable temperature<55℃ constant temperature<60℃ constant temperature <45℃ constant temperature, which indicated that the moisture in the medicinal materials was more likely to evaporate and overflow and consumes less energy than the constant temperature drying. In particular, the bias activation energy of 60-55-45℃ drying method was 77.54% and 81.86% of the other 2 variable temperature drying methods, which were 67.22%, 75.13% and 74.26% of the 3 kinds of constant temperature drying. CONCLUSION The use of cooling mode in the drying process can save more time and energy, and can provide experimental basis for the improvement of drying technology and optimization of drying process of Codonopsis Radix.