The batch extraction kinetics equation based on Fick’s law was obtained by a direct dimensionless modification with the extraction capacity factor (f1). f1 integrates the penetrating and dissolving capacity of the extraction solvent and its effect on the plant tissue. The effect of ethanol content (45%–75%, V/V) on the batch extraction of curcumin from turmeric (Curcurna longa L.) was evaluated for 3.69 mm turmeric particles at 65 °C, 80:1 liquid/material ratio, without stirring. Based on the results, and considering ethanol’s dielectric constant, surface tension, viscosity and effects on the turmeric tissue, the batch extraction kinetics equation was established using the variable separation method. The model calculations matched well with the experimental data obtained. In addition, the mechanism of ethanol’s effect on the extraction of curcumin from turmeric was also investigated.