OBJECTIVE: To study the hygroscopicity of Xuanyunding granule, and to determine reasonable conditions of humidity and exposure time in the production process. METHODS: Dynamics model was established by determining hygroscopic rate and balance moisture absorption volume of Xuanyunding granule. Hydroscopicity rates were determined and compared. RESULTS: Hygroscopicity dynamic equations of Xuanyunding granule at different humidity condition was in line with the compartment model. When absorption capacity reached 6%, relative humidity was 56.11%...