The invention discloses a method for preparing olive leaf extract, belonging to the technical field of plant effective ingredient extraction and separation. The method for extracting and separating oleuropein from olive leaves in the invention has the following steps: extracting the olive leaves by polar solvent, precipitating by flocculant to obtain centrifugal solution and precipitate, extracting the centrifugal solution, further separating by preparative high performance liquid chromatography (HPLC) for acetic ether extractive phase, performing on-line detection by a differential refraction detector, objectively collecting oleuropein product segments, performing reduced pressure concentration on preparation liquid, and carrying out vacuum drying or spray drying to obtain the olive leafextract in which the oleuropein content is larger than 90%. The invention has the advantages of simple procedures, realization of high purity oleuropein preparation, large preparation amount, high yield and good product quality and is suitable for industrialized production; and the prepared extract has no residual of harmful substances.