The present invention relates to a method of extracting useful compounds from selected species of plants. More specifically, the said method comprises delivering an extraction fluid from a delivery system to a heating means. Further, the method involves treating the plant species and the residual plant species with the extraction fluid in an extractor at the supercritical and sub-critical conditions respectively； separating and collecting the useful compounds in a first and second collecting means respectively thereby increasing the extraction rate of the useful compound.
