NOVELTY - Extracting and preparing ursolic acid from loquat leaf using sub-critical water extraction technology, comprises: (i) pre-treating loquat leaf, (ii) sub-critical water extracting, and (iii) rotary evaporating and concentrating the obtained extraction liquid, and performing the process by (a) adding ethanol into the mixture, filtering and crushing to obtain polysaccharide, (b) dissolving precipitate with ethanol, filtering, and acidifying, drying and crushing to obtain flavonoid, and (c) separating ursolic acid in the solution using non-polar macroporous absorption resin, and recrystallizing.    USE - The method is useful for extracting and preparing ursolic acid from loquat leaf using sub-critical water extraction technology.    ADVANTAGE - The method does not use organic solvent and hence it is environmental-friendly, non-toxic and natural; has high extraction efficiency; achieves multiple active ingredients by continuous separation and enrichment; and is suitable for industrial production.    DETAILED DESCRIPTION - Extracting and preparing ursolic acid from loquat leaf using sub-critical water extraction technology, comprises: (i) washing loquat leaf with water, removing hair, drying and crushing using a sampling grade, where the particle size of the sample is 0.4-0.8 mm; (ii) placing the raw materials in an extraction kettle, using liquid phase pump for deoxidizing deionized water into the kettle at a flow rate of less than 10 ml/minute, controlling the extracting temperature at 100-300 degrees C for 0.5-3 hours under the pressure of 0-10 MPa, extracting the loquat leaf, stopping the extraction process to open relief valve, cooling the extract to room temperature and flowing into a collecting tank based on the polarity (100-150 degrees C, 10 MPa; 200-250 degrees C, 10 MPa; 250-300 degrees C, 10 MPa), and collecting step-by-step to obtain three parts of extraction liquid; and (iii) rotary evaporating and concentrating the extraction liquid, and respectively performing treatment process by (a) adding the absolute ethanol to the mixture until the ethanol concentration reaches 70%, allowing the precipitate to stand, filtering to obtain the undissolved substance, drying, and crushing to obtain loquat leaf polysaccharide with purity of more than 50%, (b) adding water (3 times) to precipitate, dissolving the precipitate with ethanol, adjusting the pH value to 9-10 using sodium hydroxide, filtering using activated carbon, and acidifying, drying and crushing the filtrate to obtain flavonoid active substance with purity of more than 40%, and (c) adding water (3 times) to precipitate, dissolving the precipitate with ethanol, adjusting the pH value to 9-10 using sodium hydroxide, filtering using activated carbon, and acidifying the filtrate, separating ursolic acid in the solution using non-polar macroporous absorption resin, and recrystallizing using ethanol or methanol to obtain the ursolic acid product with the purity of more than 95%. An INDEPENDENT CLAIM is also included for a device for extracting and preparing ursolic acid from loquat leaf using sub-critical water extraction technology, comprising an operating system including a water storage tank, a pressure pump, an extraction kettle, a collecting tank and a cooler, and a control system, which is the extraction kettle of a temperature and a pressure measuring devices, and a liquid phase pump via pipeline with its one end connected to the water storage tank and the other end connected to the extraction kettle, where the pressure pump controls the flow rate of water injected into the extraction kettle, the extraction kettle connected to the collecting tank via the adjusting valve, the collecting tank places the extraction liquid to quickly cool to room temperature in the cooler, and the control system utilizes a sensing model, with its one end placed in an extraction kettle and using a non-contact sensor to measure temperature and pressure in the kettle.