Abstract: In this study,Ursolic Acid extracted from L. palustre with high extraction yield was successfully studied by the method of flash extraction. To improve the extraction yield of the Ledum Ursolic Acid in this study,a Box-Behnken design was employed based on four factor experiments. The four independent variables,namely extraction temperature,ethanol concentration,solid-liquid ratio and flash extraction time on extraction yield of Ursolic Acid were evaluated by response surface methodology(RSM). The results showed that the optimum conditions for extracting Ledum Ursolic Acid were as follows:the temperature 90℃,the ethanol concentration84%,the solid-liquid ratio 1∶25,and the flash extraction time 3min. Under the optimal conditions,the extraction yield achieved 1.52%.Furthermore,the groups and content of Ursolic Acid were investigated by FTIR,extracts containing the typical group of Ursolic Acid standard,occurs of pyrolysis reaction in the temperature range of300 ~390℃,the weight loss rate reached over 70%,the crystallinity of Ursolic sample was 64.3%,consistent with the ursolic acid standard,It was distributed in irregular ellipsoid by SEM.