Abstract: The process conditions of extracting gallic acid from Terminalia chebula Retz. was optimized with ultrasonic-assisted extraction. High performance liquid chromatography(HPLC)was applied to assay gallic acid extracted from Terminalia chebula Retz. At the same time this method was applied as indexes to evaluate the yields of extracting gallic acid from Terminalia chebula Retz. The orthogonal experiment was applied to optimize the conditions of ultrasonic-assisted extraction for extracting gallic acid from Terminalia chebula Retz. The conditions which were ethanol concentration, solid-liquid ratio, ultrasonic time and ultrasonic temperature, were investigated on the process of extracting gallic acid. The regression linear equation is A=92.48×C-28.566, which has good linear relationship with the peak area among 4(μg.mL^-1) to 20 (μg.mL^-1). The assaying condition is that column is Hypersil ODS (4.0 mm×250 mm, 5μm), mobile phase is 4% methanol to 96% water with 0.1% phosphoric acid (V: V), and detection wavelength is 270 nm, and flow rate 1.0 (mL·min^-1), column temperature 25 ℃. The optimized conditions of ultrasonic-assisted extraction, solvent are 60% ethanol (V: V), ratio of material to liquid 1: 20, temperature of solvent 50℃, extraction duration 80 min. The experiment results show that this quantitative detection method is accurate, reliable and precise for assaying gallic acid with HPLC, and the applicationto evaluating the best conditions of extracting gallic acid from Terminalia chebula is successful. The process of ultrasonic-assisted extraction is stable and feasible, and the extraction rate of gallic acid is high from Terminalia chebula.