Abstract: Abstract: As an active component in many plants, chlorogenic acid (CA) received extensive attention, for it possess lots of pharmacological activities and biological activities. Selection of suitable extraction solvent, extraction method and technological parameters is an important step to further purification and application of CA. The extraction efficiency of organic solvent in extraction of CA from Crataegus Pinnatifida Bge (CPB) is higher than that of water, but it is restricted for its toxicity causing damage to the human body and the environment. As a green and environmentally friendly solvent, ionic liquid was attracting increasing attention in the field of extraction, and ultrasonic-assisted extraction (UAE) method with the advantages of easy-operating, time-saving, energy-efficient and high efficiency was widely applied. Extraction of CA from CPB using ionic liquids as the solvent with UAE method was studied in this paper. Firstly, ionic liquid was selected from seven kinds of ionic liquids in the study, then the single factor experiments provided the extraction efficiencies of three main factors involving the concentration of ionic liquid, extraction time and solid-liquid ratio; furthermore, response surface methodology (RSM) was applied to optimize the three parameters of extraction. The content of CA was confirmed by fluorescence spectrometer with standard curve method. The results showed that ionic liquid, EImCl, was selected as the suitable solvent, and the optimum conditions were EImCl concentration of 1.19 mol/L, solid-liquid ratio of 19.67 g/mL and extraction time of 42.83 min, which obtained a theoretical CA content of 4 179.48 mg/g. Under the optimum conditions, the verification experiment of the extraction of CA was carried out with the result of CA content of 4 128.28 mg/g, which was agreed well with the regression model. In addition, separation of ionic liquid and CA was finished due to that the ionic liquid is expensive, difficult to degrade and has unpredictable toxicity. Under acidic condition, CA in the ionic liquid was extracted using ethyl acetate as the extraction agent, in which yield of CA was 96.3% of that in the extract; while the purification of ionic liquid was operated by reduced pressure distillation in the rotary evaporator, then dried at 65℃ in the vacuum drying oven, and the extraction efficiency of CA reached 92.96% when it was recycled for extraction of CA. Moreover, the comparison between the ionic liquid and traditional solvent by experimental investigation indicated that ionic liquid has obvious advantages in the extraction efficiency and recycling, and is a kind of high efficient, green extraction solvent.