Abstract: Green tea is often required to precisely regulate moisture and quality during processing. However, the conventional empirical models cannot rapidly and accurately quantify the water migration in the green tea during withering. This study aims to introduce the classic grain adsorption-desorption equilibrium equation (CAE) and the absolute water potential difference equation from the grain industry into the green tea withering. A thermodynamic quantitative model was established to dynamically predict and regulate the tea withering, including heat-moisture balance, water migration, and quality component transformation. A series of experiments was conducted using the static gravimetric method. Fresh leaves were taken as the Longjing 43 from Xiaocun Town, Xianfeng County, Hubei Province, China (108°37′8″-108°46′5″E, and 29°19′28″-30°2′54″N). The adsorption/desorption isotherms were measured in the nine supersaturated salt solutions within the temperature range of 10 to 35℃. The data was also acquired for the equilibrium relative humidity and equilibrium moisture content. The parameters of the CAE equation were fitted for green tea using Origin software. The boundary conditions were established after fitting, according to the physical characteristics of tea leaves (e.g., cell wall composition, polar groups, and porosity). Two sets of parameters specific to green tea were derived for adsorption (A₁=6.89, A₂=4.87, B₁=7.32, B₂=5.39, and D=204.5) and desorption (A₁=7.12, A₂=5.01, B₁=7.65, B₂=5.68, and D=213.2), respectively. The fitting accuracy was validated using the following statistical parameters: The sum of squared errors (SSE) values for adsorption/desorption were 1.86 and 2.15, respectively; the R² values reached 0.998; the root mean squared error (RMSE) values were 0.203 and 0.221; while the mean relative error (MRE) values were 3.12 and 3.78, respectively, indicating the excellent fitting precision of the adsorption/desorption parameters for green tea. There was a strong correlation between equilibrium relative humidity (ERH), temperature (t), and equilibrium moisture content (EMC) of green tea. The four-factor and five-level orthogonal experiment was designed using Design-Expert V8.0.6.1 software. A total of 21 experimental groups were incorporated with the parameters: withering temperature ranging from 15 to 35℃, relative humidity during withering between 50% and 70%, withering air velocity from 0 to 2.0 m/s, and withering thickness varying from 2 to 10 cm. Real-time monitoring was conducted for environmental temperature, tea leaf temperature, relative humidity, and mass changes. The absolute water potential difference between the tea leaves and the surrounding environment was calculated, along with the water migration rate (R_w). Pearson correlation analysis was also performed using Python software. There was a highly significant positive correlation between the absolute water potential difference and R_w over all treatment groups (correlation coefficient r ≥ 0.9781, P < 0.05). Thereby, the absolute water potential difference served as the primary thermodynamic driving force for water transport. The content of catechins (C) was subsequently quantified using Agilent 1100 high-performance liquid chromatography. Statistical analysis demonstrated a strong negative correlation between the time-weighted average absolute water potential difference (E_avg) and catechin content (r = -0.8429, P = 0.0001). The contents of catechin increased, as the E_avg decreased; The lower E_avg values reduced the driving force for water migration, resulting in less oxidation of catechin content and minimal quality deterioration. There was a significant influence of absolute water potential difference on the water migration rate, where the water was a crucial influencing factor to regulate the polyphenol oxidase (PPO) activity. A greater water potential difference also caused the higher water evaporation, leading to a severe imbalance in osmotic pressure inside and outside the cells. The rapid drying of the tea leaf surface also damaged the cellular structure, enabling the PPO, which was normally confined to organelles, to interact with catechin content in the cytoplasm. The interaction also facilitated the binding of enzymes and substrates. The PPO catalyzed the dehydrogenation of phenolic hydroxyl groups in catechin content and then converted them into the polymers, resulting in reduced detection levels of catechin content. Conversely, a smaller water potential difference maintained the appropriate moisture content, thus preserving the integrity of the cellular structure. Furthermore, the PPO was confined within the cells, unable to react with substrates in this scenario, leading to inhibited activity and the retention of more catechin content. The P-value of 0.0001 indicated an extremely significant correlation. Random factors were also removed for the reliability of the model. Compared with the conventional models with the static equilibrium points, there were strong relationships among thermal-humidity balance, moisture migration, and the transformation of quality components during withering. Moreover, the absolute water potential difference can be expected to indirectly regulate the quality of withered green tea