Abstract: In order to obtain the optimum conditions of ultrasonic-assisted extraction of Cyperus esculentus L. starch and its physicochemical properties, this paper studied the optimum conditions of extraction of Cyperus esculentus L. starch by single factor and response surface experiments, and studied its physicochemical properties by scanning electron microscope analysis, Fourier transform infrared analysis, X-ray diffraction analysis and DSC analysis. The results showed that the optimum technological conditions were determined as temperature 30 ℃, time 50 min, liquid-solid ratio 15:1 mL/g and pH8. Under these conditions, the extraction rate of Cyperus esculentus L. starch was 92.22%±0.99%. By comparing the physicochemical properties of five kinds of starches, such as Cyperus esculentus L. starch and wheat starch, it was found that Cyperus esculentus L. starch granules had a smoother surface than other starches, and the particle size range was similar to tapioca starch, sweet potato starch and wheat starch, which was obviously smaller than potato starch, and the particle size range was 2~15 μm, which was in the middle and small level. The stretching degree of C-O and O-H of Cyperus esculentus L. starch was low, and the stretching vibration degree of C-H was low. The crystal form of Cyperus esculentus L. starch was similar to that of most cereal starches, and belonged to type A starch. In DSC experiment, the starting temperature and peak temperature of Cyperus esculentus L. starch were only lower than that of sweet potato starch, and the ending temperature was lower than that of sweet potato starch and corn starch. The results showed that the particle size of Cyperus esculentus L. starch was relatively small, which belonged to type A starch, and it was not easy to hydrolyze compared with type B starch, and its amylopectin structure was more.